I like to think that increased competition from us (GitLab) contributed to this change, we recently passed 10m repositories on GitLab.com
At GitLab we think that repositories will become a commodity and we're focussing on making a single application for the entire DevOps lifecycle.
I think Microsoft will try to generate revenue with people using Azure more instead of paying for repos.
Also see our blog post https://about.gitlab.com/2019/01/07/github-offering-free-pri...