There's plenty of incentive for Apple to make apps plentiful and easy to acquire, but I strongly disagree that there's any incentive for Apple to want apps to be fungible. Why would there be? This is a claim I've seen repeated a few times without any supporting evidence. And I can't think of any reason why Apple would want apps to be fungible (more-so than any other software platform, at least; there is an incentive for there to be competition within any given category, but that's not the same thing as having the apps actually be fungible).

There are a lot of people who like having tons of new games available to try for a few minutes or hours or days, and then throw them away. But the existence of those people / that market does not mean that there isn't also a market for games that people stick with for a long time, and that are sold and maintained for a long time.