Nothing, just nobody made it. People always assume everything that can or should be made is already made. But that's just not the case. Get out and build stuff or else maybe no one will.

I think people just didn't realize how shitty centralized social media would become over time. They were fine for years, but the experience slowly degraded as the businesses that run them looked for more ways to squeeze profit out of their users. Eventually they got so bad that people like fiatjaf began working on alternatives. Also the idea of decentralization wasn't really thought about much before Bitcoin.

I’ll take a crack at this. I’m sure others will correct me if I’m wrong.

Like Satoshi did with Bitcoin, nostr:npub180cvv07tjdrrgpa0j7j7tmnyl2yr6yr7l8j4s3evf6u64th6gkwsyjh6w6 used existing technologies (websockets and JSON) in a novel way.

He chose a simple and fairly rigid data structure in events and chose a paradigm for relays which is (or seems to me) inspired by bitcoin. Dumb relays and smart clients.

For the network to be decentralized, the barrier to running a relay has to be as low as feasible. Like running a Bitcoin node.

Their simple data structure makes it extremely easy for developers to build applications which handle Nostr events.

Secure Scuttlebutt did all the things, Nostr is less strict

People had been thinking full distributed networks before with no central server.

fiatjaf did a hybrid. Distributed protocol but multiple independent servers (relays).

I think the difference is the simplicity of the protocol, other protocols were too strict and complex from the start. Other protocols tried to keep banning and moderation control and tried to solve everything from the start. Nostr is more simple. Nostr also took inspiration from bitcoin, with the use of keys and nodes(relays).