I feel like people making new VCSes should just re-use GIT storage/network layer and innovate on top of that. Git storage is flexible enough for that, and that way you can just.... use it on existing repos with very easy migration path for both workflows (CI/CD never need to care about what frontend you use) and users
Git storage is just a merkle tree. It's a technology that's been around forever and was simultaneously chosen by more than one vcs technology around the same time. It's incredibly effective so it makes sense that it would get used.