Apps in the Apple App Store must meet usability and standardization guidelines, and are deeply integrated into the OS. As a simple example that came up recently, all the payments on the phone go through Apple, so the payment process is the same cross ecosystem. While that is a point of discussion in the monopoly debate, it’s undeniably a simpler experience on the user side - and that translates to easy support. I don’t have to consider it it’s stripe or PayPal or freedompay or anything else when mom calls and wants help buying premium, payments just work.

With an open app ecosystem all guarantees of standardization or not using private APIs or (ideally) the app has been somewhat vetted are out the window.