I do think it's an important concern, even though I absolutely love Github. Most importantly though, `git` is not centralised, and no service like Github, no matter what it does, can ever stop the decentralisation, roll-your-own-ability, or forkability of open-source software.
So probably it's OK for now for the majority of the community to use MS's platform Github, because other options exist and it's not hard to move to them or create new ones at any time. Github doesn't own our brains, nor can it do any harm to the powerful GNU GPL.