@taylan
>Is there a technical reason Nostr couldn't have as many relays as Fedi has nodes?
There is no technical reason, but I think there's a social reason. People are not good at managing secret keys, so as the network grows, more and more people will forgo key management and will use trusted services. Basically, the same scenario that played out in cryptocurrency world. An average user don't want to think about keys and relays, so market will provide convenient but centralized solutions.
This hasn't happened in Fediverse because of the very feature you're criticizing it for. Reputation of the server can be damaged by actions of its users, and that creates a strong incentive to split into smaller communities.