social anxiety
It's not that we can't wander around places where other beings are, it's... when social things happen? The feeling of complete untetheredness of being at an event without a familiar social reference point is terrifying.
We don't go to events we want to go to. We don't have experiences we want to have. We don't talk to beings we want to talk to. We don't meet anyone entirely new.
We cling to those we do know and prevent them from having the lives and experiences they want.