I thought those people were banned?
If they were banned, and they wanted to return, they would have to change their name, because even I've discovered you can't create an account with a name that's already been used. And once registered, you can't change your name to a name that's already been used.
So your implication that they keep changing their name, for some nefarious reason, is fallacious. They have no choice if they want to continue to participate.