Think of it this way, because of the CONCEPT of trans is very recent, it's easier to manipulate politically compared to all other mental illnesses.

Everyone for centuries already had a concept for depression/manic, schizophrenia, multiple personality disorders, eating disorders etc that it's a lot harder to manipulate those conditions to a political ideology (not that they haven't tried)

Trans is so new that it was a lot easier to manipulate for the left to give more access to medical, children, workplaces, speech etc all under the guise of 'caring for a minority class'.