GP's snark is misplaced, version control is but a subset of what forges offer, git has no social layer[1], and GitHub has a monopoly on this. A distributed social layer via ActivityPub would be a vast improvement over what we have now - at best, non-comprehensive one way synching of issues from GitHub into mirror repos, by way of polling the upstream.
1. Except via email
Also: Ask yourself why did Linus "solve" VC decentralization, but not social software decentralization. Probably because one is "easy" and the other is "not obviously possible". :)
Perhaps because it was out of scope? Linux kernel diffs are emailed, so Linus solved for email as the social layer, and it works well with mailing lists. If Pull Requests had predated git and the kernel had used them, Linus would have solved for
https://codeberg.org/ForgeFed/ForgeFed
The README in both repos links to the main Codeberg repo and says that the GitHub repo is a mirror.