So first of all I don't know shit about anything, but here's what I'm thinking. There's an extant misogyny/dislike of femininity in society, such that when AMAB people want to be feminine, society looks down on it, but when an AFAB person wants to be masculine, societies like, yeah that makes sense since men are better. So a subset of AFAB people who might have had gender dysphoria, have it alleviated by being able to be tomboys or butch with less societal pressure than AMAB people who want to do femininity would get. Leading to less potential trans men realizing they are trans. But also the "nature" part of the nature/nurture composite could account for it as you've said.