GPL'd code exists, but not GPL'd art

> Art isn't analogous to code here; while you can reuse artwork in other 
projects, there is little value to be had in pulling it apart and tweaking 
the way there is with code.  If you know how to make a 3D model, there's 
not much that looking at someone else's 3D model will teach you.

Another reason for why it's not so easily reusable, is that the same 
graphics get old pretty soon. (how many games with penguins we have?)

New games need new graphics.