It cannot be stressed enough just how severely mentally ill these people are; majority untreated, and when they do seek treatment, their primary concern is someone who will validate their mental illness rather than someone who can effectively treat it; imagine if someone with brain cancer named their tumor "Bob" and refused to see an oncologist who didn't acknowledge "Bob"'s name and call him by it. Just an absolutely fucking bizarro world, ass-backwards set of priorities.
When you add in how isolated they are from real people, and then cap it off with HRT introducing poorly controlled amounts of various sex hormones into the body of someone who is already producing their own, different sex hormones, you have a perfect storm for disordered thinking, poor impulse control, emotional turbulence and eventual (even inevitable) suicidal ideation.
Does the clowning they're subject to on twitter maybe play some part? Like, fuckin', I GUESS, but tons of people are bullied for all sorts of shit, much of it a lot more deeper and cutting than using the wrong fucking pronoun of all things, and they don't immediately An Hero. It's like saying a stubbed toe is what killed a hemophiliac. Like, yeah, it contributed I guess, but there was way more going on beneath the surface that facilitated that, a stubbed toe is a minor inconvenience to 99.9% of people, and if it wasn't that, it'd have been something else equally mundane.