You're missing the difference here between "useful" and "interesting", the latter being a techie jargon word meaning "what the hell even is that" or "I ain't even mad, that's amazing."

Urbit is provably effective at generating techie amazement, and I can well believe it created enough for well-off people to spend money on address space for the amusement value (at least one has explicitly said that's why he bought some). Urbit is a legitimate mad art project, an untrammelled 200-proof expression of its creator's personality; that is in fact interesting.

This is not, however, the same as usefulness.