Ha, having been on the game dev side of this, it's _also_ often c) the teams of lawyers between the developers and the outside world won't allow collaboration.

Ha, having been on the game dev side of this, it's _also_ often c) the teams of lawyers between the developers and the outside world won't allow collaboration. The situation is _much_ better nowadays, but in the oughts and early tens it was basically a given that the game source code was considered too valuable to risk sharing.