In the context of general marketing you are right, but in the context of Apples walled garden (app store) not only is that their job, it is their reason for existing.
The more content they can get under your nose that you like, the more content you buy, the more the app devs make, the more Apple makes and the more desired the iOS store becomes.
This is why Netflix and Amazon spend millions on their reccomendation engines; same idea here.
I think you probably knew this though. I am only solidying the point that inside any app stores environment, it is the job of the owner of the store to markwt the content effectively. Outside the store, anyone can do anything they want.