1) Apple's App store revenue may have seen a decline recently...Can someone explain why the App Store needs ads? What is the point? Who benefits?

App Store experienced sharp revenue drop in September, Morgan Stanley says | TechCrunch
Apple's App Store net revenue declined by 5%. It's biggest dip since Morgan Stanley started tracking the data.

2) The point of ads is to make up for the revenue shortfall
3) This benefits Apple and their shareholders