I think it's about solving problems. UX is important but remember that at some point in time, the concepts of a username and password and email address were very foreign to everyday people yet email still achieved mass adoption. I think the problem email solved more greatly outweighed the novel UX. 

For nostr, people who care about digital sovereignty and decentralized social media are coming/have come. They don't care about the UX. Normies don't care about digital sovereignty and decentralized social media and so for them the UX cons outweigh any benefit. Normies will come once nostr solves a problem for them.