> People saying that it is easy to migrate don’t know what they are
  > talking about. GitHub isn’t just Git hosting, but a social network
  > of open source developers and projects. You can’t migrate stars,
  > issues with comments and the history of PRs, all linked to the
  > profiles of their authors.

Every single for-profit company works their ass off to build a "moat" around their business and to create switching costs, even if they boast that you can "just take your data and leave."

It is not an accident that it is difficult for non-trivial projects to "just leave GitHub." That is by design, it is part of how it grew to become the 800 pound gorilla, and it is part of why Microsoft bought them.