Github is not something that most devs use much of the time. It is really there to provide the open source code for the public. Any real dev is using a Git server of their own to share with the team or, if there is no team, they may not even need to have up to date code in multiple locations or they use a simpler method.
Git also has some private repositories and Enterprise solutions.
Note: 100% of the devs I know use Github, and mostly the main site with private repositories. (I am based in the Silicon Valley, maybe it is not representative of the global dev community... at least the US one, or maybe I know only bad devs... still overpaid here :-))