Similar as they may appear, the comparison between Steam and Apple's AppStore is disingenuous.Valve doesn't prohibit developers from selling the app directly to customers and installing the app on their devices, bypassing the middleman. Apple absolutely locks down iOS devices and direct installation of anything is impossible (testflight and MDM options do not count).

This makes these two appstores completely incomparable. Enrolling in one is voluntary, and is done by developers because it is beneficial to them, another one is extortion.