I think there are valid technical and usability reasons for demanding that all products within a store all conform to the same billing policies. For Apple, providing a consistent user experience is absolutely paramount. They want all apps to act the same and bill the same. If the baseline/standard experience is sub-optimal, then they would say let us fix or improve the baseline experience for everyone, not deal with it piecemeal and leave the user guessing how an app will end up billing them.
In this case I think some users are looking for a double opt-in in the case of a free trial, or at least a native reminder in the iOS user interface that a trial is ending and the first subscription charge is about to be run.
For example, if the day before a trial expired, you could receive a push notification from Apple notifying you that the trial period is about to expire, and how much you will be billed if you do not cancel before the end of the day. Alternatively, the push notification could require active user consent before allowing the trial to convert to a paid subscription.
The first option could be done by Apple with zero required action by developers, but since it's definitely going to increase the cancellation rate, probably developers aren't going to be very happy. It is customer-focused which Apple claims to be, but it's also messy/cluttered to be getting billing notifications
The problem with the second option is that it opens up a new state in the state machine, and three new transition functions. Going from trial -> pending approval is a mid-state which would require some sort of shutting off functionality in the app or even preventing the app from opening, or reverting back to the unpaid / non-trial state. Now the user is in a new limbo 'pending approval' state. Then from there somehow the user has to either approve the charge or indicate that they do in fact want to cancel, so going from pending -> unsubscribed or pending -> subscribed are new transitions that would have to be coded for every app.
The current solution is to simply provide a centralized place to see all your subscriptions and when they will renew and how much they cost, and making it single-tap simply to cancel them. I'm not sure a better way they can surface the Subscriptions UI other than within the App Store settings. That top option within 'Settings' always seemed misplaced to me, it looks more like a header than a button, and especially as it is encompassing "Apple ID, iCloud, iTunes & App Store" it's kind of a jumble. They added it into the App Store app as well on the top-right profile-picture button which leads to 'Account' and then 'Subscriptions'.