Epistemic status: Jeff missing the point
The supermarket sells various kinds of fancy butter, but why don't people eat whipped cream instead? Let's normalize to 100 calorie servings and compare prices:
- Plain Butter, store brand: $0.10
- Heavy Whipping Cream, store brand: $0.20
- Fancy butter, Kerrygold brand: $0.30
Perhaps the reason people don't normally use whipped cream is that whipping it is too much trouble? If you use a manual eggbeater in a standard sixteen ounce deli cup it takes about fifteen seconds (youtube) for a serving.
Alternatively, maybe people think whipped cream has to have sugar in it? This one is simple: whipped cream should not have sugar in it. If you're eating whipped cream on something sweet it doesn't need sugar because the other thing is sweet, while if you're having it on something savory it doesn't need sugar because that would taste funny.
I'm sure I'm missing something, but I'm very happy over here eating whipped cream.
You can keep butter in your fridge for weeks and it will stay fresh enough to use. (If you're fussy you can scrape off a thin layer of slightly-oxidized butter from the surface.) You can't do that with cream. That doesn't matter so much if you have shops where you can conveniently buy fresh cream every week, which is pretty common these days but maybe used not to be.
As others have said, cream contains a lot more water than butter does. If you spread whipped cream on your toast, I'm pretty sure you'll get soggy toast.
Butter keeps approximately its consistency for much longer than whipped cream does. If you make sandwiches with whipped cream and take them to work or school for lunch, I'm pretty sure you'll end up with not-at-all-whipped cream making your sandwiches soggy.
If you're specifically buying fancy butter, you may want the flavour of fancy butter. This is not the same as the flavour of whipped cream. (Just how different depends on exactly what sort of fancy butter.)
It's not so easy (I think) to whip up cream in very small quantities. That "serving" looks to me like a distinctly larger amount of cream-or-butter than I'd want in contexts where I'm using butter but not cooking with it.
Generally, I'm not very sure why you would use whipped cream instead of butter. I mean, OK, it's a bit cheaper (if you ignore wastage and effort and so forth), but so are many other things: water, flour, sawdust. And while clearly whipped cream is more like butter than water, flour and sawdust are, I don't see that it's so much like butter as to serve the same purposes. It doesn't have the same taste, the same consistency, the same balance of nutrients, the same anything.
UHT for cream isn't as bad as it is for milk, and it can be done more or less well, but typically all the cream at grocery store, including the organic stuff, will be UHT: https://www.peapod.com/product-search/heavy whipping cream