If your remote goes down but you have an email based workflow, you can continue as if nothing happened. One could argue that your mail server might go down, but it’s better than having your centralized GitHub-like forge go down for two reasons:
1. If not all contributors use the same mail server, it’s much less of an issue since not everyone goes offline at the same time. Additionally, your maildir doesn’t care whether or not you’re online; both the git repo and all mailing lists have offline copies distributed to all collaborators out-of-the-box by default.
2. GitHub’s reliability is significantly poorer than the vast majority of email providers. The great thing about decentralization is that getting good uptime on a small mail server for under 1000 users is much easier than getting good uptime on a centralized forge re-implementing email’s features for millions of users.