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.
It's OSS, so if you want to do something similar but without GH branding nothing stops you (assuming you have enough cash on hand to pull it all off).