Unlike, say, the phone network, it doesn't actually cost you anything more to throw up a git repository on any number of free-speech-supporting websites, including many that offer substantially the same features as GitHub. You can still reach the same people without dragging your own cable half way across the planet - you just don't get to steal someone else's reputation in order to make it easier to do so.

The other side of things is that many websites actually want (algorithmic) editorial control over what their users wind up seeing because that's more profitable for them, and if they want that, they're definitely in a position where choosing to promote content is a direct reflection on the company even by your standards. GitHub is, as far as I'm aware, not one of these companies though.