Because of tropes like tvtropes.org/pmwiki/…/CreepyCrossdresser from movies like Silence of the Lambs, Dressed to Kill, and Psycho. It puts the idea of men dressing like women as a means of tricking women to attack them into the collective unconscious.

Because Trump spent $19 million on transphobic ads during football games in battleground states. Because they need a Boogeyman to rile up their base.

It doesn’t have to make sense. You might as well be asking how can the KKK hate people of color or how can Nazis hate Jewish people.