Its difficult to pin point.

Bad UI is what annoys me the most. Something like i2p, would be great, but none of the i2p apps are user friendly at all.

Signing up to nostr with primal was really easy, but even then, there's no real explanation of what lighting is, what's the deal with wallets? Etc etc. I knew a lot of it as I've been involved in similar before, but most people would just walk away.