It seems like a simple solution to me would be to make the game free, but with most features blocked behind a SINGLE in-app purchase. That way you can download it, play what amounts to basically a demo, and decide if you like the game. If you don't, you've lost nothing, and the game developer gets the opportunity to add an additional step to their funnel and see how many people genuinely don't like their game or are frustrated / confused by it. If you do, you buy it with the IAP and now have the rest of the game forever.

What am I missing here? Is this hard to do? Or prohibited somehow?

Disclosure: I'm not a mobile game developer, so maybe I'm missing something here about the rules of the app stores.