It’s a given that the more GitHub features you use, the more difficult it is to move away from GitHub. It’s also a given that you can reasonably limit the extent to which you use GitHub and thereby limit the difficulty in transitioning to another solution.
The idea that it’s GitHub locking you in rather than you locking yourself in to GitHub is the argument I take issue with. But no quarrel at all with Gnome choosing GitLab, because GitLab is genuinely great.
The whole reason GNOME wanted to switch is because they wanted to have all the extra features (issues, etc) in a single place, as is provided by Github and Gitlab. Their old cgit interface already did a good job at hosting their git repositories.
Well, some people do. I don't, apparently you don't, probably most people don't. But you could and some people do. I've seen a few projects on github with notes to the effect of "don't bother submitting issues/PRs here, do it through our [mailing list/etc]"
It's logical of course, but I see the irony. Or maybe it's not irony, nobody really knows what irony is, but it's mildly.. amusing? It makes half my face smile in a manner similar to but not quite like a smirk.
Definitely not 'expected'. I like the mailing list bug tracking more than having that on git{hub,lab,whatever}.
git makes it even possible to host a repo on multiple git* hostings, but apparently nobody came up with a successful distributed pullreq/issue tracker yet.
You don't use github just for git.
You use it for issue tracking, pull requests and code review, CI hooks, wiki, github pages, kanban boards, bot integration, and so on.
That's all stuff that locks you in to Github, and is non-trivial to migrate to another provider.