From my experience, it always follow the same path. Some promising developer gets infatuated with Apple's supposed ease of use and looks at the shiny aggregate numbers like $155 billion paid out to developers. Said developer jumps through all the hoops and builds a great app. Users love it, but since competition in the app store is insane, the developer barely makes back his/her initial investment. Then Apple changes the APIs and rules, the app becomes unusable and/or expensive to maintain and over time the developer burns out and gives up. Thus, there's now an opening for the next promising developer to start building an app.
As long as Apple doesn't run out of new developers happy to join the App Store, they can treat their 3rd party "partners" as badly as they want. It's kind of the same power dynamic that makes sure that hair saloons all over the world treat their employees badly.