That would be true if enterprises had their own local git repositories, and if employees pushed against those local git repositories. But this is not what happens, when enterprises use github, employees directly push to github.

Continuous integration tools directly pull from github.

When github is down, all exchange of patches between employes essentially halts, as does continuous integration and testing.

Of course, this is not the fault of git.

This is the fault of people keeping using centralized servers, instead of setting up and using their own local servers.

The same goes for email (gmail anybody? Really???)

The Internet is meant to be a decentralized, peer-to-peer, meshed network. Not a centralized, star network!!!