I can't tell if you're joking, but if not I use it because it's a reliable, free git server.

Not sure why you’d think that. Maybe this is common in your circle but I don’t know anyone who uses github just to host a remote repo.

You literally have to pay to have a private repo. It isn't just a common use, it is feature you have to pay for.

Github's social/discovery features are too strong - it makes it difficult to justify keeping OS projects on GitLab even if the feature set is better for maintainers