The whole point if git is decentralized, it's just not doing it in a BitTorrent style DHT internet protocol (yes there are ways of connecting git this way).

Git is a way to keep files organized and revisioned across many connected or disconnected computers. It literally was designed to allow software development between teams and individuals that have no centralized organization and via any file-copy medium available including thumb drives. It was essentially an upgrade to managing software codebases with zip and patch files, which worked adequately for many decades. After Linus had some experience with a centralized VCS, but was still distributing his software in zip (tar.gz) files, he decided to write his own VCS so the community wasn't dependent on the existence of one corporation. He sat down and outlined a basic set of requirements for a VCS software that would do what he needed. Interestingly bitcoin's first revision was stored in git, and git was used to coordinate and secure the codebase around the world. You can go back to this first commit in the bitcoin-core repository and see what the first alpha version looked like.