Seems to me like a lot of them have stuck around. Don't personally know how or why.
Some of them get banned a lot too, but come back every time none the less, is perm banning nonexistent anymore? Is there not some sort of X strikes and your out rule? And even when perms bans are issued i still see people who have been perm banned just appeal after a few months or years.
If they insist on being dickheads or trolls, why give them so many chances? Everyone can change or deserve a 2nd 3rd or 4th chance, but at what point does it end?