I always assumed it was more or less targeting the federation of issues/MRs.
The git side of things is already distributed as you said, but if you decide to host your random project on your own GitLab instance you’ll miss out on people submitting issues/MRs because they won’t want to sign up for an account on your random instance (or sign in with another IdP).
This is where a lot of the reliance of GitHub comes from, in my opinion.
This is pretty much how I am, too. I’ve purchased SDV three times but could never get into it because I have no idea what I need to do.
Big fan of the dev though and how much he does for the game, even if I don’t personally play.