GitHub is centralizing all those features. If GitHub was just for repo hosting, then you would need to link your repo to another platform to do CI, another platform for issue tracking relative to the code, etc.
They have those features but those aren’t decentralisation issues, as far as I’d understand the term, but those already can be done elsewhere right now. They’re purely tied to one repo really, it’s only the user accounts that I can see being more of a cross repo concern.
And global search but I don’t feel like that even really works.