That's not the only reason people use Github. It's the Facebook of programmers in some sense and it's got a critical mass that switching to something else is not practicable (not without some serious momentum).
I think this is an unfair jump because they do have a legitimate business model with enterprise revenue - they don't need to start owning your life to continue to exist.
The "Facebook of programmers" is a great analogy. Because while the masses act like they cannot live without it, those of us who just don't use it really do not feel like we are missing anything in our lives.
There are other Git services. There are other source control mechanisms. There are other ways to do things. Just like you can actually leave Facebook, feel free to leave Github. Or stay. But make a conscious choice.
This is a distributed source control system. Keep a clone of the repo somewhere. Your source code is now no longer bound to Github.