Because it's easier for potato-headed autists to take a cursory look at a Disney channel sitcom meant for girls and think THAT'S what femininity is. Actually trying to understand every conceivable nuance there is to being a woman and thus, making a cogent effort at trying to pass is WAY too hard a concept for most troons to actually grasp. The idea that "presentation =/= gender" is pure bullshit and it's only used to justify why a fat man in a shitty wig with dollar store lipstick should be viewed as a woman. Sure, presentation in and of itself does not necessarily equate to gender, but it's still a HUGE reason as to why we can still recognise tomboys as girls and bishonens as men.Christ, why is it they are all ugly, fat, pervy looking munters with ratty hair c/w bad taste in clothes? Selection criteria?
On a slight tangent, I notice this type of behaviour a LOT more in trans women than trans men. At the absolute bare minimum, an FtM trans person is still able to grasp the concept that not all guys are into cars, skeet shootin', bodily noises, mud 'rasslin, and bikini babes. Trans women more often than not just hang onto this caricature of femininity that they slapped together from all the stereotypes they've seen on TV and the internet and if someone dares call them out on it, you get the whole "reeeeeee presentation =/= gender bigot reeeee" spiel.