This claim gives an impression of being unfalsifiable. Any counter-example could be dismissed as the person being either insufficiently self-aware, insufficiently motivated to work towards a goal or not really desiring a 1:1 relationship.
I have seen people make similar claims in a way that is not falsifiable. That isn't what I'm going for. Let's see if I can make the terms a bit more concrete:
What kind of evidence would lead you to conclude that this is not as rare as you suggest?
A significant number of people dedicating 3 hours a day for 3 years to the goal of developing social skills and sexual attraction ability and not being able to form a relationship. With that much effort it is extremely improbable for someone without significant mental or physical disability to fail and it would be enough for even most people with moderate disabilities to have quite good odds.
Is insufficient self-awareness an impediment you think people could also overcome if willing to develop and work towards a goal or is it merely a convenient label for people who prove unable to get a 1:1 relationship if that is their desire?
Self awareness usually comes with time and maturity. You know, realizing how you act, etc. I include self awareness because obviously anyone who doesn't realize (or admit to themselves) that they want to achieve a goal or notice what results they currently get will not even bother trying. The people you mention seem to already have plenty of self awareness. If they don't then they are extremely lucky and someone else has input the relevant goal while they were on auto-pilot.
One more thought: Doing a lot of something doesn't always make you better at it. There's practice, and then there's meaningful practice, and you need meaningful practice to get better, not just any practice.
For example, suppose you're a poor writer and you're trying to get better, so you set out to write more stories. However, after spending a lot of time writing, all that happens is that you've become better at writing poorly; you don't suffer from writer's block any more and can finish a story much more quickly than you used to, but each individual story...
Many of us are familiar with Donald Rumsfeld's famous (and surprisingly useful) taxonomy of knowledge:
But this taxonomy (as originally described) omits an important fourth category: unknown knowns, the things we don't know that we know. This category encompasses the knowledge of many of our own personal beliefs, what I call unquestioned defaults. For example, most modern Americans possess the unquestioned default belief that they have some moral responsibility for their own freely-chosen actions. In the twelfth century, most Europeans possessed the unquestioned default belief that the Christian god existed. And so on. These unknown knowns are largely the products of a particular culture; they require homogeneity of belief to remain unknown.
By definition, we are each completely ignorant of our own unknown knowns. So even when our culture gives us a fairly accurate map of the territory, we'll never notice the Mercator projection's effect. Unless it's pointed out to us or we find contradictory evidence, that is. A single observation can be all it takes, if you're paying attention and asking questions. The answers might not change your mind, but you'll still come out of the process with more knowledge than you went in with.
When I was eighteen I went on a date with a girl I'll call Emma, who conscientiously informed me that she already had two boyfriends: she was, she said, polyamorous. I had previously had some vague awareness that there had been a free love movement in the sixties that encouraged "alternative lifestyles", but that awareness was not a sufficient motivation for me to challenge my default belief that romantic relationships could only be conducted one at a time. Acknowledging default settings is not easy.
The chance to date a pretty girl, though, can be sufficient motivation for a great many things (as is also the case with pretty boys). It was certainly a good enough reason to ask myself, "Self, what's so great about this monogamy thing?"
I couldn't come up with any particularly compelling answers, so I called Emma up and we planned a second date.
Since that fateful day, I've been involved in both polyamorous and monogamous relationships, and I've become quite confident that I am happier, more fulfilled, and a better romantic partner when I am polyamorous. This holds even when I'm dating only one person; polyamorous relationships have a kind of freedom to them that is impossible to obtain any other way, as well as a set of similarly unique responsibilities.
In this discussion I am targeting monogamy because its discovery has had an effect on my life that is orders of magnitude greater than that of any other previously-unknown known. Others I've spoken with have had similar experiences. If you haven't had it before, you now have the same opportunity that I lucked into several years ago, if you choose to exploit it.
This, then, is your exercise: spend five minutes thinking about why your choice of monogamy is preferable to all of the other inhabitants of relationship-style-space, for you. Other options that have been explored and documented include:
These types of polyamory cover many of the available options, but there are others; some are as yet unknown. Some relationship styles are better than others, subject to your ethics, history, and personality. I suspect that monogamy is genuinely the best option for many people, perhaps even most. But it's impossible for you to know that until you know that you have a choice.
If you have a particularly compelling argument for or against a particular relationship style, please share it. But if romantic jealousy is your deciding factor in favor of monogamy, you may want to hold off on forming a belief that will be hard to change; my next post will be about techniques for managing and reducing romantic jealousy.