You do know what's a mailing list right? You seem to be confusing it with GitHub.

A mailing list can go down and nothing would happen. The main point is to post patches to the maintainer. The mailing list is for a public record of things.

The only centralised thing is repo hosting on kernel.org. And that isn't the only official place, you can get the repo published on googlesource or GitHub, so it isn't exactly central enough.

I contend that if you submit a patch under any circumstances your change isn’t going into linux today.

I suppose that's true. In any case, though, getting a backup mailing list going is much much easier than something like GitHub, and you can always mail patches directly if maintainers allow it.