Most of us work for companies that owns the code we develop. As a result most of our best accomplishments are not public.
You can use GitHub when you looking for graduates (i.e. one might expect that the better students would do something on GitHub to learn), but I don’t think it is a good place to evaluate seasoned developers.
PS We don’t have trade unions because if we had that it would be the crappiest of us who would benefit with a detrimental effect on salaries of those of us who are already earning nice salaries during our higher skills.