The bottleneck is content, especially RPGs require a lot: Art, models, sounds, music, dialogs, story, gui, level design, etc. And everything in a consistent sty

The bottleneck is content, especially RPGs require a lot: Art, models, sounds, music, dialogs, story, gui, level design, etc. And everything in a consistent style otherwise it looks too cheap. Multiplayer games require little content relative to play time. Single player do though and thus there are only very few open source ones.