Yes they're pretty hard to rehome. They're everywhere and the shelters are full of them. Usually they stay a bit longer unless they have something really unique about them.

They also tend to be dogs who are either dog reactive, prey driven (want to chase and eat small animals), or just can't do multi dog households. That's another barrier since they often need a one dog home with someone willing to put in work.

Then you have home insurance banning them making renting harder.

There's a lot more barriers to keeping/adopting a pitbull/bully mix than some random fluffy dog from the shelter.