And that's not even starting with the questionable morality of using GitHub in the first place (~ after Microsoft bought them)... (especially for non-US developers)
Yeah, leaving aside other concerns about platforms, Microsoft, and the USA, I too want to stress how GitHub is problematic in GP's «some metrics are bad» sense : the social networking aspect, stars, number of projects, and, as you say, number of contributions and number of lines of code.