So at least we can agree that all the points about how they give you the app store, IDE, push notification service etc. are all bullshit and this is only about not blocking users' access to an app.

Regarding that, it comes down to the long history of general purpose computing - users buy a device, users decide what goes on it. The entirety of today's software ecosystem, and pretty much all of the internet as it is only exists because people were able to run and publish whatever software they chose, host whatever webpages they wanted, without the end user's device's manufacturer having any say in it. Apple likely wouldn't exist today without all the software that was created as a result of that either.

Imagine if they did the same for websites - removed access to the open web and only allowed you to visit approved websites, and also took 30% of each website's advertising and subscription revenue in addition. If they could get away with something like that, they totally would. The only thing that's stopping them is that people wouldn't currently tolerate that.