Git is a distributed version control system. It is built specifically to NOT have a backend at all. (as opposed to SVN and others that had been popular before) All clones are equal. 
It happened that people used GitHub services. Now people don't know Git and don't care about reading up on it. 

Imo chances are high, that the same will happen with Nostr. If successful we will all use the same relay and will blame Nostr is not decentralized.