Because they think nothing through. It doesn’t occur to them when they say trans women will rape girls in bathrooms that cis women can rape girls too. It also doesn’t occur to them that forcing everyone to use the changing rooms of their biological sex because “women are uncomfortable with a man changing next to them” means that they will be changing next to people who sure as hell look like men what with the no breasts and the beard. I’m guessing that will make them a hell of a lot more uncomfortable.