There are very few people who would opt in to a editor for everything only to use it with Github. Most of the world's developers don't even have a Github account.
Tools work in a strange way. I recently saw a whole team of embedded developers use TextPad. They haven't heard of anything called 'vim' or 'emacs'. From their perspective its either a vendor supplied IDE or TextPad. One of them was even startled to see this shiny new thing called 'Sublime Text' when I was using it. He went out with enthusiasm, but was hardly able to convince any one to use it.
A code editor with first class prominent Github support is more likely to encourage creating Github accounts - it would just work. Compare to regular code editors which require jumping through various hoops (typically having to find relevant plugins, install them on all machines/users, and then figure out how to use them as they are extensions not core).
A pitch of "if you use this editor then all the team's work is automatically synchronized and available" is a very powerful sell.
Tools work in a strange way. I recently saw a whole team of embedded developers use TextPad. They haven't heard of anything called 'vim' or 'emacs'. From their perspective its either a vendor supplied IDE or TextPad. One of them was even startled to see this shiny new thing called 'Sublime Text' when I was using it. He went out with enthusiasm, but was hardly able to convince any one to use it.