A restaurant has to cook a whole new meal for every customer. An app developer does not.

But chefs and developers both need to eat their own meals every day, which they need to pay for.

An "App" isn't like a book or an album that you make once and it remains unchanged forever. We have the word "abandonware" for a reason. If you want decade-long binary stability from platform owners, bug them about it. But even just things like unforeseen changes in device formfactor, or external third-party API changes, all these things mean that unmaintained apps rot and apps that are maintained shine. You can't get sustainable income from just new sales forever, unless your app is incredibly mainstream - and the only apps that are that mainstream are owned by huge corporations and monetized through advertising anyway.