There’s a significant amount of people that have never met a trans person (or at least a trans person that didn’t pass), so it’s just foreign and scary to them. Think of it like a horror movie (to be clear, I’m not comparing trans people to horror movie creatures): the movie is more suspenseful and scary if we’re only able to see the creature from the shadows for a decent chunk of the first act. When a horror movie shows the the creature right away, the horror has to come from somewhere else. I think the idea is to take away the fear by presenting trans people to transphobes without endangering trans people.