Forcing Apple to implement interop and such extra features requires a non-trivial amount of labour. That trickles down to the customer in many subtle and not so subtle ways that the parent comment mentioned (more resources and higher inter-dept. coordination ceiling for a streamlined UX, etc.)

Comparing it to opinions about gay marriage makes you look dishonest, "None of this is about you, at all" makes you look plain silly

If Apple somehow implements interoperability perfectly, sure. But I don’t believe that they, or anyone else, can. I’m sure any API will have unforeseen consequences and bugs, and those will affect me.

And I don’t really get to opt out either as eventually I’ll be forced to update my software.

Well, I happen to like that any service I subscribe to using my phone can be unsubscribed in one click, without jumping backwards through hoops while standing on my head begging customer service to cancel and no I don't want to extend my trial at a special discounted rate. And the iPhone market is big enough that companies have to offer signup in their app. But if companies start drifting to only offering services via other stores or payments, then they will inevitably fuck up the cancel option again, and I will lose something.

Sounds like that should be required by law, not the whims of an abusive monopolist.