Simplicity. Pubky tries to solve the indexing problem of where to find people's data from the web of servers out there. Nostr just deffers that to a NIP.
Discussion
What is the indexing problem?
Finding which server has which event is a massive computer science problem. Nostr solves it by using relay hints of where things could be. Pubky uses a DHT protocol underneath.
"defers that to a NIP" as in "leaves it to the client devs to figure out". We don't have consistent standards and your feed looks different on different clients. Some find stuff others don't find.
It emulates real life, honestly. And that gives it an edge by being aligned with nature rather than opposed to it, trying to make global state a thing.
I see it the other way around; a global state will always want to emerge from these kinds of networks, and trying to fight the emergence of that global state is like trying to fight nature itself.
Nostr already has a de-facto global state as a result of private parties crawling and indexing the full network. Not a perfect global state of course, but close enough, and one that enables faster loading, advanced search, accurate follower counts, and much more.
I'd estimate that over 80% of Nostr revenue—as in what could be claimed as income on a corporate tax return—is going to parties that are crawling and indexing the whole network. The parties that are not indexing the whole network are fighting for the remaining 20%.
Slowly the fruits of these indexing efforts, being so tasty, will work their way into all clients, and the fruit juice will seep everywhere, and from that point forward calling Nostr a network with "no global state" will be merely lip service to a glorified past.
This always happens. As if nature demands it. Well *human* nature anyway.