To an end user there’s an icon on their screen, they tap it, the app opens. It didn’t matter if they downloaded from the AppStore or from a website. This is no longer the case which is why the OP is upset.
Phones are computers. Even if you remote all connectivity to the outside world, they still function as well as any PC from the early 90s (or earlier). A huge amount of compute power, tons of storage, etc. etc.
Yes, you as the user could wipe those out. But now Apple is doing it just because you didn't use it in 7 days. And the user will not blame Apple, they won't even know Apple did that. They will blame the app developer, who in the interest of privacy didn't want to push your personal Todos to a database online.
Again, just a contrived example, please don't go down the road of why a server should have been used. Let's stick to the use case described.