But the ranking is not reflective of actual skills. That's the critique. Aside from very frequent open source contributors (and I think these people are the minority of devs), devs will tend to be "profiled" by this tool according to the dot scripts, university projects, Advent of Code, or other half-hearted projects they happen to have put on their Github. (Maybe I'm just projecting...)

The issue isn't that not everyone has a Github presence, the issue is that for most people their Github presence is somewhat unrepresentative of their actual job skills.