Re ground zero: i honestly think gay marriage becoming legal has something to do with the transtrender wave in particular, since now just being gay seems lame and mainstream compared to being trans. If it were 2005 the same types of people would be loud about how bi they are. Bruce Jenner might have opened the AGP floodgates. There's no one moment, but those two things stand out to me.
I remember seeing a comment on reddit that basically summed up how the massive rise in trans and non-binary identity within the last few years amongst youth is largely because of how limited the opportunities to partake in any sort of cultural transgressions are nowadays.
I imagine weed is just kind of boring now that it's being legalised in America. As in like alcohol, teens are still using it for fun, but there's no longer a 'culture' around it. Most harder drugs are either too expensive and difficult for teens to get a hold of (coke, acid) or scary and uncool (meth, crack).
Most kids have their own laptops or smartphones by the time they have the slightest interest in porn, so there's no risky act of buying magazines/vids or silently rubbing one out in front of the family computer in the middle of the night anymore.
Even though teenagers are having less sex, it's become incredibly normalised and socially acceptable, to the extent that many parents make no effort whatsoever to prevent their children from fucking. Anti-slut shaming norms have also made getting slutty way less fun, and social media means hot guys and girls have to compete for attention with thousands just like them on Instagram/TikTok/OnlyFans.
Veganism? Catered to at almost every store and eatery.
Tattoos? Piercings? Mainstreamed.
Are you a man with long hair or a woman with short hair? No one cares.
Fuck the police? Fuck the government? Fuck America? Fuck God? All boring, uncontroversial opinions at this point. At the very least, there is 0 risk involved in expressing any of these opinions in much of the West.
There's just no real source of friction left, so kids are forced to create their own sources of it. To be clear, I don't think this applies to every young person who come out as trans (definitely the case with non-binaries tho), but it seems hard to deny that it's happening to a large degree.