It's for attention and control. By being trans they get a popularity boost, they become "special" people with new privileges and abilities, like being able to go around and scold everyone and make everyone treat them differently.
Like how a motorcyclist gets to swerve between lanes, squeezing through traffic jams, that's what it's like for trans people in society. They get to walk over everyone because trans people are given like this golden key to become untouchable, ordinary norms and laws don't apply to them.
That's what the trans movement is all about, it gives them instant attention, control, and superiority.