But trans very much was cool, and still is according to a lot of genderist propaganda. The colourful flags for gender identities, the coming out "celebrations", the special clubs to join, the vilification of "cis" people as boring normies, the platforming and promoting and special attention. I agree distressing things can also be social contagions, but a trans identity was definitely promoted as the cool things to be including in schools.
5 years ago, aged 10/11, my DD and all her friends had special LGBTQ identities for about a month, and bought the flags and shared them out. It was frowned upon to be straight and cis so nobody was. My DD chose bi. Some chose trans boy or NB. None of them have those identities now but if they'd parents or teachers who wanted to run with it and push it, they could have gone down that path easily.
I remember the "trans boy" staying with the other girls on a school residential trip and the (older, female) teachers being extremely sensible and sensitive about it while ensuring she was safe. But that's not always what happened.