I think that's mainly cultural, actually. "Github is down" is seen as "take the day off". But it actually is pretty easy to work around a remote being temporarily down. Developers can use their local copies of code and merge them when the remote is back up. Or whoever has the latest commits can start a temporary git server in an EC2 instance and tell the developers on slack to update their remote URLs.
Of course, if your build process is tied into github actions or something, that will still be broken. But that problem also exists for any other 3rd party build/deploy service you might use, independent of git-the-VCS-tool.
Yes, that's my point. It doesn't matter if your protocol is decentralized as long as your business processes rely on having a blessed authoritative repo, which most do. Yes, you can point your remotes somewhere else, but in practice nobody bothers.
Of course, if your build process is tied into github actions or something, that will still be broken. But that problem also exists for any other 3rd party build/deploy service you might use, independent of git-the-VCS-tool.