People don't wanna talk about it at all because it's too close to trans-ness being a mental illness but imma come at this from entirely the opposite direction:
The NO.1 predictor of a cluster B personality disorder is a consistently invalidating childhood environment.
What's more invalidating than spending your whole childhood saying "hey I think I'm actually a-" and every single person around you cutting you off right there and saying "no you ain't." Psychiatry ain't shit without social context but psychiatry is also coming to accept that being constantly invalidated as a child gonna do your brain the fucky-wucky.
It's ok to accept that trans ppl are at an increased risk of personality disorders due to our completely fucked societal norms. Accepting that we're at increased risk of mental disorders due to societal bullshit =/= saying being trans is a mental illness. If anything, it's an indictment of the society we live in.
TLDR; trans ppl are at increased risk of mental illness =/= transness IS a mental illness and we still deserve to acknowledge the trauma society done did to us.
I appreciate your take on this and I wish we were talking more explicitly about this in LGBTQIA+ spaces. The theory of how bpd develops is complex and probably includes biological factors (think, brain differences leading to sensory issues, memory issues, etc which then lead to certain experiences being more challenging to recover from) but you are correct that the experience of trauma and invalidation in childhood are central to the development of bpd. If we have a society that uniquely traumatizes trans folks, it makes sense that more trans folks than cis folks would have bpd as a result.
One of the more disturbing facets of some of the new anti-trans legislation in US states has been language that seeks to make it impossible for someone autistic or someone who has a personality disorder to access gender affirming care.
This ableist language is clearly the next line of attack and serves to dehumanize not just trans folks but also folks with personality disorders and neurodivergences. Anyone who thinks that these governments intend to stop at murdering trans folks is a damn fool - these laws make it clear there are other groups they intend to target.