I agree. If it was just the relay/key model that was holding Nostr back, the Fediverse would be massive now. But people tried Mastodon instead of Twitter / Kbin instead of Reddit and very few people stayed.
Having to manually curate your feed means it's just less compelling.
I love Mastodon and check it once a day lol. My Facebook buddies have it open in a tab all day. It's addictive by design.