I kind of get it. Here's why:
The average viewer has been hit with a litany of anti-trans rhetoric. They would have to cope with their feelings about all of this if they were compelled to watch a movie that doesn't demonize or ridicule trans people. Well, that's not a lot of fun.
Sort of like seeing a movie or documentary about hard-working immigrants. "I was told that it's ok to drag those people off to immigrant prisons without a trial. Why are you showing me this side of the story? It's very inconvenient."
Hollywood financiers want to make money and stay out of controversy. It seems that a movie that portrays trans people sympathetically might not do so well.