Unfortunately for utopianists, self-interest is how things get done that would otherwise never get done. It powers most open source work.
If a company or individual does something just to slap their name on it, so be it.
The combined open source effort vs Github's effort shouldn't be compared as it doesn't make sense. Just like it doesn't make sense to compare the work of a translator vs. the work of writing the original material—the translator is still doing valuable work regardless. The translator isn't "taking credit" for the original work.
You should compare what Github is doing with other endeavors doing the same thing.
This is the most real case of cultural appropriation in the last decade.
But the corporate smoke screens focus on bogus cultural appropriation and related issues, so this one will yet again go unnoticed.
I'm thinking about updating my OSS licences.