The rent seeking trickles down to customers. See Netflix not taking subscriptions through Apple anymore. If this happens with one service, customers may be puzzled, if this happens with all services, customers will get annoyed. The way Apple treats their developers is how they treat their platform.

The apps and iCloud portion of my comment should be relevant, as is the observation that I can't load whatever I want on the phone. I have to go through this horrible app store which Apple took years to redesign and ended up being even worse than its predecessor for discovering content (and policing content!)