Git, or any file-server based software, is not built to scale up well in today's world. Large Git hosters have to invest entire teams to manage their file servers and their Git front-end systems to create a web-scale service on top of a file-server based piece of software. I'm just skipping to the part where you don't need that anymore because Azure / GCP / AWS PaaS services already handle that.
And, in any team dev situation, you're not getting anywhere until you `git push`, and that requires an internet connection. Assuming ~100% connectivity for devs around the world, in the late 2020's, is the right assumption to make. If offline is a hard requirement, Git isn't going anywhere.
> through non-http transports like mail
yeah, I'm not building a new VCS for that 0.0000001% case.