I commented earlier about this, yes you are correct with Microsoft allowing you to get games outside of the Microsoft Store, but both Nintendo and Sony restrict digital games through their consoles to their store only. You cannot compare the ability to use physical game disks in consoles and the Apple App Store because there is no physical thing for the App Store besides like gift cards.
You need to compare that just like Nintendo and Sony (where Sony even has the digital only PS5) those app stores only allow games to be purchased from their store. Sony used to be more lenient but they have since shut those
down. Sony for a few years now have stopped the purchase of digital game codes being purchased from retailers, so for instance, the digital only PS5 (the cheaper one) basically you are restricted to whatever full price/sales that Sony wants to give.
*I will put the disclaimer that yes a consumer can purchase a digital key from a person from like G2A but this comes with it's own risks and IMO cannot be counted*