That's the thing - git was fundamentally a tool borne with an asynchronous workflow in mind: I work on X, Alice works on Y, Bob works on Z, and the eventual merging (which might happen days or weeks later) should be as simple as possible - without worrying about who checked out what. Git was dropped in the "distributed VCS" bucket, but decentralization was a secondary effect of the workflow Linus wanted to achieve.

GitHub then took the server-side bits of git, and effectively built a web-based interface with social features on top. Git itself is still very much a decentralized tool (just add a new remote and off you go), only the social GUI is centralized.

It would be cool if somebody could build "Github over P2P" (I guess with a bit of blockchain, because hype). At that point the entire stack would be fully decentralized.