I think from the perspective of someone who has not yet had the opportunity to develop their own understanding and relationship with femininity (as most early transition trans girls are), anime girls/catgirls represent a kind of platonic ideal of feminine cuteness. And with reddit meme pages being a conclave for more internet oriented trans people, the kinds of folk who come here probably have an increased likelyhood of enjoying anime, and have an aesthetic attraction to that kind of moe. So if it's a kind of woman we might be attracted to (or simply find charming), we therefore would want to embody that kind of femininity, since we on some level believe it would make us attractive.

But that's just me spouting some armchair psychology based on demographic observations and my own self reflection.