Because, you can register their key. When they buy the game, they can be given a code. You can ban the code or the key. That way, to play the game, you'd be required to buy it again. That is the best form of protection for a BYOND game, but who is going to buy a BYOND games, and if the game is good enough to be bought, who is just not going to buy it again?
Hey, I wonder if Kajika has something like that. in theory can't a game be programmed to asign each Byond application with a "hidden" identification number, that is placed in a non Byond file(so it can't be located), therefor downloading a new Byond application has no affect. He does say that he uses another ban system in addition to the ones I listed.
well feel free to try.