It is not a win win for consumers when an app that is essential for you forces you to download their app from a third party app store. You are assuming that apps like facebook, etc would offer an app both in the App Store and some their own third party facebook store, yeah right. They will make you download it from their store and skirt all the Apple privacy rules. That is just one example. same thing with bank apps that don't want to pay apple fees for Apple Pay. They will FORCE you to download their apps from a third party app store.
This hasn't occurred with Android, why do you think iOS will be different?