I don't think anyone really knows......
Ideas
1/ USA libertarianism. The ultimate liberationism, in a free market anyone can be anyone. That includes remodelling your body to reflect your "soul".
2/ USA capitalism. Can the American health care system be trusted on this? When they make a profit out of making physically healthy people dependent on drugs for the rest of their lives.
3/ Queer Theory. Boundary pushing, to change a society that they see as centering people who are heterosexual or haven't got gender dysphoria. Power struggle by those who "feel" oppressed.
There are also those in this group who wish to erode boundaries around age of consent. Like PIE in the 70s. Eroding women's sex based rights helps a certain type of person too.....
4/ Finding a tribe /rebellion. There's definitely a social contagion element to all of this. Young people especially want to fit in with the Rainbow. It's belonging to something and now the letters are as long as the alphabet, anyone who wants to can. The QT elements are the only thing my kids and I disagree about, nothing else to rebel against. It is almost spiritual with holy days, and months of observance. Maybe humans need that? To believe in something beyond science eg humans can change sex.
5/ There is no doubt the Internet has magnified and sped up social changes of all types. Protests seem more fragmented and niche, as the culture wars heat up. And yet the rich get richer and the poor get poorer.
6/ Mental health. I do think the worsening of mental health, especially amongst the young is a factor. Our lack of understanding of neuro diverse people doesn't help either.
7/ Puritanism. "The surest way to work up a crusade in favor of some good cause is to promise people they will have a chance of maltreating someone. To be able to destroy with good conscience, to be able to behave badly and call your bad behavior 'righteous indignation' — this is the height of psychological luxury, the most delicious of moral treats." Aldous Huxley
8/ Virtue Signalling. Politicians and institutions definitely saw this as an easy win. Get brownie points from the youth and all you've really got to do is open the loos to all comers.
9/ Homophobia. In fundamentalist religions it seems to be better to trans away the gay. We've seen this frequently in some cultures and it was mentioned in by Tavistock whistle blowers.
10/ Keeping the lobby group staff paid. After the great battles for equal rights for LGB people had been won, what next for the Stonewalls of this world. They've literally built an industry out of all this.
Two fictional works look at what's going on: Simon Edge in the End of the World is flat has a right wing billionaire at centre.
Ben Elton, in Identity Crisis, has the Russians as the cause.
Kathleen Stock is good on the emergence of the queer theory sex is meaningless nonsense.