Tbh I think all of you are partially correct in trying to pin down the chain of unfortunate events/experiences/psychology behind what drives young women to transition. In my experience, FTMs seem to be steadily overrepresented in many fandom communities, and while many are homosexual/bisexual, a majority have an intense fixation on gay male relationships (realistic or fictional). However, they tend to be more well-adjusted in my IRL experiences.
I subscribe to the idea that it's a combination of their generation being exposed to degrading porn WAYYY too early, because it absolutely depicts sex in a way that is quite removed from anything women are typically brought up to anticipate in romantic relationships, particularly straight ones. I would go as far to say it completely distorts what is a normal aspect of human behavior and twists it into something solely about power rather than mutual pleasure and enjoyment.
Not to mention teenagers are fucking stupid and puberty is extremely uncomfortable, and hearing your male peers discuss humiliating sex acts that they viewed casually in a classroom is absolutely jarring/frightening and can lead to a crippled understanding of what sex even is.
Coupled with a budding sexuality (that
@Corn Flakes was describing) that manifests unhealthily due to all of the negative associations these women/girls will come to associate with sex in general, it creates an understandable incentive to want to escape a destiny they may feel little control/agency over.
In a lot of ways these girls probably never had a healthy way of processing their own sexualities and sought refuge in fictional relationships between societal "equals" that they could manipulate and characterize all on their own (BL, yaoi, shipping & that aspect of weeb culture in general).
EDIT: This alone however does not explain the prevalent idea that homosexuality suddenly doesn't exist because they believe they are literal men. I have a lot of empathy for FTMs, not because I see them as perpetual victims who lack agency, but because I see them as literal women whose psychology and development are given little consideration, especially given the overlap I've noticed with eating disorders/body dysmorphia & dysphoric women. However, the ones who believe they become gay men have #mento-illness.