1. It is way easier to steal something and resell it convincingly, than it is to prove original ownership convincingly. This tilts the market in favor of thieves, as they need to do none of the investment and still reap maybe half or more of the total potential income.
2. Apple pulling something from a store should affect only a fraction of a normal market; instead, it affects literally everyone.
3. Gatekeepers such as Apple win regardless of who sells an app. If a developer complains and Apple has millions of alternative developers/apps, why would they even listen? The motivation is simply nonexistent.
These problems would all be nullified by abolishing the concept of a single gatekeeper store.
If you can easily steal something but there is no easy place to publish it to get stolen revenue from “nearly everyone”, the value of the theft is reduced. (Imagine if you had to find a way to propagate your stolen app to 100 stores. Would it be worth it?)
If you can convince one storefront to accept your stolen app as legitimate but you still have to convince a bunch of other stores, the value of the theft is again reduced.
If each store has a relatively smaller chunk of the total market, none of them would want to become known as that store where crappy apps make it into the list so they would be more motivated to curate a decent catalog.
The same obstacle would also apply to all legitimate app developers…