I've commented this elsewhere, but Apple encouraging users to only upgrade and purchase subscriptions through Apple's payment systems and hiding in-app alternatives and links to other options isn't just about the 30% fee. It also increases consumer lock-in to the Apple ecosystem.
If the only thing you're using your phone for is calling, browsing, and buying apps, it's not that hard to switch to Android. You lose all of your apps, and that stinks a lot, but if most of your apps are free you might tolerate that. And outside of the apps, you can keep your phone number, export your contacts, etc...
But if suddenly all of your phone subscriptions including newspapers, music services like Spotify, hosts like Wordpress, email services like Hey, and so on -- if all of those are only managed through your phone and can't be canceled or upgraded by the companies themselves then that's another big annoyance to deal with that might keep you from switching just because you want an Android app that isn't available for your phone.
Apple tries very hard to lock users into its ecosystem. That's why there's a credit card now that only works with Apple phones; it's to make sure that if you ever change phones, you now have to deal with canceling a credit card. That's why companies aren't allowed to build their own interoppable solutions around iMessage. It's to make sure that if you change phones, you get social stigma from your friends and have a worse SMS experience with them.
The payments rules are another part of that. Yes, of course Apple wants the 30%, but they also want literally everything you do on your phone to be tied to them. If Apple could create a world where you lost your phone number when you switched phones, they'd do it in a heartbeat.
They want their walled garden to have a one-way door.