They are spending time and money to prevent that. Or you can create an app store as an app and expect Apple to allow your "app store app" to ship in iPhones? The features are already there in the OS, they use them themselves. They dont need to do anything more.. but instead they work to cripple or prevent others from using it.
This is in essence the spirit of a monopoly.
Ok you personally dont mind for whatever reasons, but there a lot of other harms to the society and civil rights in general going on here. And that was the reason countries and laws exists.. To prevent people or companies in position of power to abuse their power.