[astrange]

Open-sourcing commercial code can be difficult because it might contain or use things from other companies that you don't have permission to release.

Of course, it might also just be that you don't want your employees to get any fame, but they do seem to be allowed to talk at GDC.

[avx56]

Yeah, I think it's that and the fact that there isn't (obvious) money in fixing up and maintaining code for a shipped game.