You don't need a 'multi-million dollar budget' to self-host a git repo and may of these open-source projects have been doing so even before GitHub existed for years. Even if they did have such a budget, there isn't an excuse left to self-host and avoid going 'all in' on GitHub.
At the very least I would expect something like what ReactOS is doing by having a self-hosted backup just in case GitHub goes down or vice-versa. [1]
Looks like that is proving to be useful.