Most of the people I grew up with who went the trans route were always...uhh, "different". One person who comes to mind we literally always knew was at the very least gay, from the time I met him at like age 3. Far as I know he had a normal home life, though he got called a faggot so many times growing up I'm sure it probably left a mark. Never saw him get bullied other then that but where I grew up I wouldn't be surprised. If you're a little boy and you hang out exclusively with girls and have a full on queer eye for the straight guy lisp by the time you're 5 I don't know how much you can attach it to upbringing by itself. Him becoming "her" I think was just the logical next step in his lifelong journey of gradually intensifying faggotry.
That said I think the internet has really destroyed a lot of people's grounding in reality, and coupled with the overall decay in
community life in the US that's been accelerating since Reagan a lot of people are being left isolated and rootless. I think sexuality for most human beings is a pretty fluid entity, the "this or that" thing is kind of a myth. Our closest relatives in the animal world fuck literally anything that moves and I don't think we're any different on the whole, but we are more reflective and we have all this other cultural and interpersonal bullshit in our heads that regulates our behavior. The concept of "sexual identity" doesn't exist to a bonobo, it does to us. We're too smart for our own good.
People people are increasingly left to their own devices in the neoliberal era however "identity" is sort of collapsing. People are desperate for anything that puts their experiences into perspective and allows them to be a part of a community. Human beings are a social species living in a pathologically anti-social environment. I don't think what explains the general rise in transgenderism is "trauma", most trans/queer people I've met are actually middle class white kids from good homes who have never experienced an actual day of hardship in their lives. We just have no grounding in any sort of meaningful cultural or personal experience, there's no connection to other people that helps us shape ourselves.
We spend most of our time alone, in our rooms, staring at screens, and being bombarded with incoherent and contradictory information about "how things are". That's our environment. And it's leaving us desperate for something to make us feel like we belong. Gender is easy, because it doesn't mean anything and it comes with a ready made community of people who will kiss your ass even if you don't deserve it.