See I'm not convinced it is a huge group. I've got a couple of trans and non-binary friends and they are all disgusted by the way these loud trans activists carry on. Apparently in their trans circle the bullying activist types are really disliked.
Interesting, but might be coincidence.
I have met quite some trans and non-binary people on the internet, and they're all misogynist asshats who either scream "TERF! Die in a fire!" when someone politely disagrees with their gender ideology, or cheerfully and without feeling bad about it side with such a person.
(Coincidentally all those utterly disgusting people are part of a group I used to be somewhat friendly with. Or, well, I was friendly with them, they obviously lacked any positive emotion towards me.)
The only decent trans people I've met on the internet were the few who sided with women-identified women on mumsnet. And interestingly, those were all males, if memory serves.
I haven't ever met a transman who didn't ultimately turn out to hate women.
Some transmen want a biological child of their own, that's probably all there is to it. No need to look for ulterior motives.
No one said females who get pregnant have "ulterior motives". One simply wonders what their alleged maleness consists of, if it is neither dysphoria about their female bodies, nor about preferring the male set of stereotypes to the stereotypes forced on women.