If your a small company developing something closed source is there any reason to use GitHub over just setting up a git infrastructure on your private server?
All that isn't trivial to setup or maintain, so small folks especially will often find it cheaper and faster to pay M$ for all that.
If you are a small software company, presumably your code is your most important asset. You should be self-hosting that, then you can know exactly where it is and whether it's actually backed up and you can instantly talk to the person who is responsible for it.