I don't know what's the reason behind why Qatar wanted to host World Cup because it's probably not the money they are after because they are already petrol nation which economic doesn't need some more boost as with or without World Cup, their nation is already rich enough. And I doubt if they after the tourist because from my perspective, they aren't much of a tourist friendly nation.
When you have endless money, then you want something intangible like fame, world recognition, etc. Otherwise, why are these sheikhs competing in crazy projects (including buying up European football clubs)? It was something from the same area. It's not economics, it's closer to politics where rational considerations don't work.