They have been building it for some time and it has different goals and tradeoffs
https://chatgpt.com/share/67fe08fe-33c4-8009-8f22-d0e80fc267a3
Discussion
I'm not saying Nostr could fill the function they strive for, but there are some overlap. Key handling -- Nostr has infra for key storage, signers, etc. 'Home servers' - light server which you can (and should) run yourself for Pubky -- maybe Nostr relay infra could do the same.
The DHT lookup, app logic, that's specific and new.
I'd be more sympathetic if there was some kind of synergy between Nostr & Pubky. Looking from a distance, Nostr also has to do with decentralized web/publishing afterall.
We have tried interacting with Nostr people over the years, but they aren't really interested in outsiders. Partly for competitive/tribal reasons, but also because the most interesting differences we have would be breaking changes for Nostr (but worth it imo, hence why we build anyway).