The way I've heard it is this: People tend to use the same sorts of social media as the gender they were assigned at birth. Or, to put it another way, they don't change social networks when they discover themselves and/or transition. Reddit and its descendants Lemmy and Kbin are dominated by AMAB users, and therefore see more transfem users than transmasc users. I'm assured there are a lot more transmasc people on Tumblr.
There's no reason to expect symmetry in gender dysphoria experienced by AMAB and AFAB bodies. There are no strong evolutionary pressures creating that symmetry. I've seen surveys in the U.S. reporting ratios upward of 6:1 transgender women to transgender men.
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.
Interesting theory. I wonder if society was more accepting of femininity in men, we'd probably see fewer men taking the nuclear option of full mtf transition. More of a spectrum from hyper masculine to androgynous to feminine, like we see with women.
Obviously I can't say anything for sure as this is speculation, but I have heard at least one trans woman say that part of the motivation for facial feminization surgery was in being able to pass better and being accepted in society as a woman. So perhaps if society was more egalitarian in how men vs women are valued, less demanding that AMAB people fit their assigned gender role, and/or gender roles are abolished then we would see at least some portion of the "why transitioning will help" equation be reduced. Though I think there's reason to believe even if gender is abolished and there's no social pressure one way or the other at all we would still find AMAB people who are significantly more comfortable in a female presenting body and vice versa and in the middle too (and I'm lumping together any combination of hormones + top surgery + bottom surgery here, in whatever form they may take in the future). So a spectrum as you said.
Are there any evolutionary pressures pushing anything? Symmetry is essentially the default, I'd assume. Isn't the ratio of gay to lesbian roughly the same?