I'm no Stallman, but I'm deeply uncomfortable with how readily everyone is accepting (and encouraging) GitHub as the complete overlord of open-source software. As already pointed out, Sourceforge is a cautionary tale of how these services can go very wrong due to business issues. There's also a much larger philosophical issue with basing the open-source economy on a proprietary platform with no particular intent of open-sourcing its core software.
Yes, GH does a lot of things right, including generally making it easy to export data form their apps in a reasonably vendor-neutral form. But what happens when GH runs into financial trouble like SF did? Do we want just about every project out there to have to struggle to do something with their GitHub issues?
There are issues with having open-source projects maintain their own infrastructure, but I think it's the right thing to do wherever possible. It makes them truly independent in a way that a GitHub repo can never be.