I thought your question was regarding ppl who self identity without requiring any outward physiological changes.
Rigid gender roles benefit and uphold patriarchy. So a patriarchal society will naturally embrace sex change (gender change) rather than try to dismantle sex stereotypes.
The liberal left get a new extra special oppressed group to fawn over to prove their stance on "inclusive and accepting" (at the usual expense of women of course)
It's taken Northern America by storm partly because The American medical industry benefits hugely from being able to forcast $$$ in artificial hormones, puberty blockers, potential surgery, hair removal / hair implants etc and a lifetime of medical intervention from one patient.
It also appeals hugely to the narcissistic youth who gets to experience lots of special attention, praise about how "brave" they are and also get to verbally abuse people who think it's not quite right. In the past they'd have just got a tattoo or whatever.
It's no coincidence that in America and the UK youth levels of psychosis are on the rise at the same time as neoliberalism rising, huge gaps in wealth and equality on the rise, and narcissism is on the rise, transgenderism is also on the rise.
Being trans is one way for u underlying mental health problems to present.