[learc83]

Yeah but if I use this GPL licensed code as the basis of a new game, I have to release the source code for my new game as well.

The vast majority of game studios aren't willing to do this, so effectively releasing it under the GPL means that it's much less likely that a competitor uses the code.

Asset flips from other countries with more permissive (or just hard to access for foreigners) legal systems are already a problem for game developers--releasing the source code for your game would ensure that you'd be inundated with assets flips almost immediately if your game is any good.