I'd argue that at least their API indicates they try to reduce rather than reinforce this lock-in. The API lets you build tools like https://github.com/colmsjo/github-issues-export to automatically export data from issues and other project data stored outside of git.
Moving this data is still not trivial but I don't think GitHub could unilaterally make it much easier.
Moving this data is still not trivial but I don't think GitHub could unilaterally make it much easier.
(https://developer.github.com/v3/issues/)