All of the bullshit f2p apps out there generate incredible revenue for Apple. Clash of clans alone generates 1M/day. That's 300k/day Apple gets for doing nothing.
Apple would have to give up that free cash.... Not happenimg.
The App Store generates such an insubstantial amount of cash (for Apple, as compared to their other platforms and products) that it would be completely insane for them not to focus on the long-term quality of the store — which would be a driver for their hardware sales.
I am absolutely certain that they realise this, but it just happens to be an incredibly difficult problem to solve without basically rejecting 90% of the apps that get submitted.
Where by nothing you mean "run the App Store".