- Curation history is crippled: Games are a piece of cultural history, and if you care about curating that history, then a complete release is important.
- Learning/Derivation is crippeled: Releasing works is about being able to learn and derive from them and to release what you've done with it. There are more kinds of people than coders, and there is more to a game than code. You can learn and tweak assets in many meaningful ways as well.
- Practice of Culture is crippled: Derivation is also about re-contextualization and remixing. Code can be remixed by programmers, and by programmers only. However sometimes remixes of content are interesting, for instance as a total-conversion of the code to something completely different (webgl for instance) or by re-contextualizing the assets entirely (you could make it props in your next CG movie).