> one day they just go poof and everyone knows why.

I thought the point of ban waves was precisely because there's no direct cause-and-effect. E.g., if you perform an exploit and get banned immediately, you know that the system can detect your exploit. If you get banned a month later, it might have been your exploit or something else you did between then and now.

This reduces the selection pressure on black-hats to produce ban-avoiding exploits.