Other possible explanations:
Your recipe is gluten-free because you made it so. Any biscuit can be made gluten-free if you choose gluten-free flour, so the question 'why do companies not sell more gluten-free biscuits?' is not specific to this recipe.
I made a batch. I used exactly the quantities specified. My pinches of salt are probably larger than average. I mixed the flour, salt, ginger and NaHCO3 together and sifted them. I used a soft cake/pastry (wheat) flour and good-quality European butter. My ground ginger is rather old and probably less flavourful than it should be. I cooked them for about 14.5 minutes at 170 degrees in a fan oven; they are probably somewhat overbaked.
They're nice biscuits. They're definitely not obvious improvements on (good home-made) chocolate chip cookies, peanut butter cookies (I make these but add 100g of chopped-up dark chocolate), or Ottolenghi-style "florentines" (which are not in any useful sense florentines but are delicious). Mine came out a little greasy, perhaps as a consequence of overbaking (or maybe my butter has a higher-than-usual fat content?).
If I'm comparing against other home-made biscuits, I think a sufficient explanation for the fact that these haven't taken over the world is that they aren't obvious improvements on other sorts. (Though they do take less effort to make than many others.)
If I'm comparing against mass-produced shop-bought biscuits, I think it's the factors other people have mentioned: good home-made biscuits will not stay good on the shelves for months, and they use relatively expensive ingredients.
[EDITED to add:] In view of Pazzaz's comment that they're much better when warm: I had some more several hours later. They aren't obviously much worse (though I wasn't eating them straight out of the oven to begin with) but I will say that they seem a bit dull. Perfectly tasty, quitte more-ish, but not all that interesting. If I made them again, I might use treacle in place of golden syrup, darker sugar (I used half "golden caster" and half "light brown soft"; caster(UK) = superfine(US)), more spices, etc.
Further update: today my wife ate one and said, unprompted, "These are good." She is not usually given to such outbursts of enthusiasm :-). I asked whether she likes them better than other kinds of biscuit I make (which I think are particularly good, else I wouldn't bother making them) and she said maybe. She specifically disagreed with my judgement that they're a bit boring. So, one data point in favour of the hypothesis that for some people these are unusually tasty biscuits.
Swedish perspective: It's pretty funny seeing these biscuits praised as some kind of perfect recipe/secret treasure when it's one of the most common biscuits here. And when I say common I don't mean that they can be found in stores or cafés (though they sometimes can) but that it's something many people make at home. I think the reason that they aren't more common in stores is that they taste much better when they are warm; from the oven. The stores can't compete with that.
The recipe I'm used to is pretty similar to yours (from the famous Our Cookbook) but without the ginger or salt.
I think this is almost entirely about shelf-life.
Yes, these are probably more expensive to make than Oreos, but that just means stores would stock them in addition to cheaper cookies. Some people would buy expensive-but-good cookies and some people would buy cheap-but-terrible cookies.
The problem is that the shelf-life for these is probably only a few days at best, and I doubt they'll be that much better than cheap cookies even a few hours after baking. Try wrapping some in plastic wrap and leaving them on the counter for a week and see if you'd still pay 3x what you paid for the ingredients for that cookie.
There are bakeries all over the place that sell good cookies (I'd guess about 1 bakery with good cookies per 30,000 people). But your supermarket probably doesn't stock them because of high expense and shelf life of only a few days (all that golden syrup is hygroscopic, which I suspect would be the primary culprit, though maybe fragility or the fact that real butter spoils would be more important.)
I think the comments so far are focusing too much on the biscuits, and not enough on the free market. The conundrum, after all, is not the biscuits themselves, but rather their apparently counterintuitive absence from the market.
I'm sure the biscuits are good, fantastic in fact. But the free market is absolutely inundated with food. Food is an easy problem to solve: everyone needs it and everyone likes it, and every civilization throughout history has unsurprisingly churned out thousands of varieties of it. A single average supermarket will contain thousands, if not tens of thousands, of different foods to choose from, no doubt including several hundred types of desserts and pastries. Many of these foods are outstandingly delicious, many arguably more than capable of maxing out the pleasure circuitry in the average consumer's brain.
So we can sort of shift the burden of proof: instead of asking why these biscuits aren't on the market, perhaps it's easier to ask why they should be on the market given all the other foods already there. As mentioned, it's not difficult to please consumers with food, and although each food is unique, the satisfaction and pleasure gained from it is not. Do we have any reason to believe these biscuits offer an amount of pleasure that is not already matched by 1000+ other foods already available and in mass-scale, efficient production?
Is gluten free flour here motivated by making them tastier or is it about avoiding gluten? Says wheat flour 'will do' but not any white flours?
Making them tastier, though not confident about this - originally motivated by not having normal flour, and then have done some of each, and thought the gluten free ones were better, but much randomness at play.
I did mean 'white' by 'wheat'; sorry (I am a foreigner). I haven't tried anything other than the gluten free one mentioned and white wheat flour.
I interpreted "wheat" as "made from wheat" rather than as "wholewheat", so I don't think there's any suggestion that white flour is inappropriate. (The ones I made were with white flour, and they seem to have turned out OK. I would expect wholewheat flour to be worse rather than better, but not with high confidence.)
I suspect the water content of honey/treacle (estimating 15-20%) will lead to more gluten formation, which risks causing a chewy instead of crumbly texture. (If you're not adding any water at all, you're not getting gluten strands.) Butter also has some water (around 15%), so you generally don't knead these kinds of dough for long. (Same goes for shortbread, scones, ...)
Hence, I guess any flour should do if you know how to handle it / are careful not to overwork the dough.
Laura made them with white flour as a breakfast. She thinks she underbaked them, I do not think this. I also had to stop her from letting them sit too long, because everyone always lets everything sit too long.
The two of us plus two kids had half of them.
My verdict is that they were a good product and distinct from the things we usually eat, and I'm happy we made them. Above average for sure, but also not the best thing in its general reference class we've made. They are not something I would want to make often, as I think repeating them would make them less tasty.
Agree with others that these being fresh and hot added a lot (as it always does) and I expect eating them several hours or days later would not be exciting.
Strong encouragement for others to post other such things in the future.
The most obvious explanation is that home-made biscuits are just better than industrial biscuits - due to better quality ingredients and less concern about transportation/conservation.
I finally got around to making these! I was very pleased with the result, they were tasty and distinct from anything I've had before. While I thought they were about as delicious as most homemade cookies, my partner who is not generally a huge fan of cookies liked them much more than previous cookie attempts and kept coming back for more.
I agree with the other commenters who've suggested that like with most homemade cookies, they're better than store-bought cookies because they don't have to last for months on a store shelf. But I am surprised it's not a more popular home recipe in the US as it's about the easiest recipe for tasty cookies I've come across.
The most obvious explanation is that home-made biscuits are just better than industrial biscuits - due to better quality ingredients and less concern about transportation/conservation.
A more practical explanation based on seeing the recipie, I'm very bad at baking, so I can't cook it:
Crossposted from world spirit sock puppet.
I saw a picture of these biscuits (or cookies), and they looked very delicious. So much so that I took the uncharacteristic step of actually making them. They were indeed among the most delicious biscuits of which I am aware. And yet I don’t recall hearing of them before. This seems like a telling sign about something. (The capitalist machinery? Culture? Industrial food production constraints? The vagaries of individual enjoyment?)
Why doesn’t the market offer these delicious biscuits all over the place? Isn’t this just the kind of rival, excludable, information-available, well-internalized good that markets are on top of?
Some explanations that occur to me:
If you want to help investigate, you can do so by carrying out the following recipe and reporting on the percentile of deliciousness of the resulting biscuits. (I do not claim that this is a high priority investigation to take part in, unless you are hungry for delicious biscuits or a firsthand encounter with a moderately interesting sociological puzzle.)
Kolakakor
(Or Kolasnittar. Adapted from House & Garden’s account of a recipe in Magnus Nilsson’s “The Nordic Baking Book”. It’s quite plausible that their versions are better than mine, which has undergone pressure for ease plus some random ingredient substitutions. However I offer mine, since it is the one I can really vouch for.)
Takes about fifteen minutes of making, and fifteen further minutes of waiting. Makes enough biscuits for about five people to eat too many biscuits, plus a handful left over. (Other recipe calls it about 40 ‘shortbreads’)
Ingredients
Method
Bonus mystery: they are gluten free, egg free, and can probably easily be dairy free. The contest with common vegan and/or gluten free biscuit seems even more winnable, so why haven’t they even taken over that market?