Hello,
GPL states if you want to make a game using even a little bit of their source code or art, you need to redistribute your project as well. Sometimes releasing your own source code makes your game easy mode to be hacked. For this reason I wouldn't want to release my code initially at release, but I'd release maybe down the road a couple years.
What I want is a licensing system where I can use someone's code/art for free, but if I make a profit, cut them a share. Right now there are systems that make you pay up front, and if you have no money to begin with, you can't do that. But if people made a licensing system that said,"Pay us 1-50% of your revenue in royalty", I'd be all over that.