According to Abigail Shrier in her book Irreversible Damage, a lot of these people look at porn at a very young age, get a warped idea of what sex is like from it, and start to think “if that’s how people have sex then I don’t want that” thus the “soft cute boy” identification begins as an opt-out from being perceived as a sexual object. And it’s not just porn anymore - as the culture becomes more open about sex, popular culture becomes more sexualised and these same tropes and stereotypes end up in mainstream music, films etc., young people who take interest in this mainstream stuff emulate it, and those who don’t begin to think there’s something wrong with them.
Mostly applies to the female ones (who are the subject of Shrier’s book), understandable as women in porn often aren’t portrayed favourably, though I can also see a dorky awkward teenage boy being unable to relate to mainstream portrayals, not realising it isn’t accurate to reality, and taking on a non binary identity as a way to escape those expectations just as a girl would.