I honestly don't understand why anyone uses GitHub for professional projects. It's inferior to not only GitLab but also Bitbucket.
I don't think it's just a familiarity thing; I've been using it for months and still haven't adjusted. Gitlab's UI/UX has gotten better by leaps and bounds, and I prefer it to BitBucket, but it still feels like it has a ways to go.
Why move unless there's a compelling reason to?
I don't care about the integrations on Gitlab because it already has everything I need, plus they ship new features at a rate of more than one per decade.