Epic tried distributing Fortnite via side loading on Android and gave up, and ended up crawling to Google to get on the Play store so we’ve already run that experiment and it failed badly. Stores are vital for discovery at commercial scale.

Bear in mind Apple didn’t have to do a store at all. Steve Jobs was against the idea and wanted all iPhone apps to be in house from Apple only in order to maintain quality. Alternatively Apple could have implemented APIs and services for side loading apps like on Android. They chose a middle path, and why shouldn’t they? Are the two extremes really the only options that should be tolerated?