I don't think it has to do with demand as such. It is just hard to allocate resources with business class only flights. With a traditional layout you can oversell economy and upgrade or push people to the next flight. If you are running all your business class capacity on a few flights you can't do that. Nor can you have the same amount of routes. I guess you can say that is because of demand, but it is more because of the model. "Tourist business" doesn't really exist, unless maybe we count Norwegian.

That said, I would love to see an all business Airbus A321neoLR with Thompson Vantage Solo seats.