Like I said, I haven't had much experience with trans people irl as far as people who I knew were trans. It's harder for them to project that status in person unless they have some obvious indicator, which is either not passing convincingly or otherwise some kind of shirt/pin/merchandise type stuff of the flag, or just outright stating it.
The ones I've run into consistently online though have always seemed to fall into another category of those who fetishize the opposite sex, usually in relation to anime/cartoons/etc. Like several of the "muh yaoi" type people I saw running around fandom 10+ years ago are now trans men and for some totally incidental reason, adopted characteristics of their husbandos, just like MtF often do with their anime waifus. It does exist for both sexes, not just MtF, though I think there is a higher volume going from male to female for reason #2.
I suppose it's possible those people always were trans at heart and just gravitated toward characters they felt reflected their "ideal", but I have a feeling the topic is probably more just about blatant self-hatred at heart, or maybe internalized hatred of their gender. For men this could be people like Chris who felt like they weren't masculine or didn't attract the attention of women (the classic "I became my waifu" thing), maybe for women they desire the power/status men can have. Makes me think of Randy Stair again, as far as I know he never voiced or showed any indications of being trans until he became fixated on his waifu, which seemed to be an extension of him wanting to escape a life he didn't enjoy, maybe he thought being a girl would be a better life. I don't think it's always strictly about gender but also about the lifestyle that one perceives the opposite gender can enjoy (usually not very rooted in reality either). Randy and Chris also both were heterosexual men before becoming trans, so it wasn't about escaping being gay.