Github succeeded because they have build a fantastic platform, order of magnitude smoother, better looking, easier to use and faster than any of the similar projects. Try to navigate http://sourceforge.net/ or http://code.google.com/intl/pl/ for a while to get a feel of how free VC hosting looked like before Github - nobody approached the problem with a normal (in the industry) professional product design approach, it was just developers throwing things together, those are almost showcases for how bad developers can be at user experience design when left by themselves.