I fail to see what makes games any different from other software. The piece of software can be easily studied and tinkered with, users have the power to control what exactly runs on their machine, and the software can organically be improved by people making their changes in their own derivations of that software that they make available for the whole world to use, study, reproduce, and modify.

Furthermore, if the developer dies, the game being FOSS will guarantee that it will live on and continue to benefit future generations.