The main function of GitHub is really just advertising or at least broadcasting your work. I would use GitHub issues, stars, etc as an (imperfect gauge) of the quality of a library. This is not because of GitHub's features, just that it's the biggest and most well known. And yes I know buying stars is a thing, which is why it's part of the evaluation and not the whole ballgame.

Now that zig is fairly well known and trusted, it makes sense that this is less of a concern for them when migrating away.