As a developer considering working on a subscription app, I strongly believe that a user should be able to cancel their subscription in as few clicks/taps as possible, in the most discoverable place possible, no questions asked (other than a confirmation).
It’s my opinion that the median user would first think to undo something they did (like start a subscription) in an app by opening that app. That’s especially true now that IAP is branded as Apple Pay in the sheet that’s presented when you’re asked to buy something. But right now, Apple doesn’t allow that, instead forcing many (most?) users to Google “how to cancel subscription iphone” and similar queries before they find out that they have to open either the App Store or Settings to cancel a subscription that they started in a specific app. Then it becomes “oh, I’ll just do it tomorrow,” and then it rebills, rinse, repeat.
Since Apple’s taking a cut, Apple makes it easy to start giving them money and difficult to stop. That’s sleazy.
Edit: Speaking of which, why do you think Apple waited until a PR firestorm erupted to start cracking down on apps that charge $9.99 a week for a simple PDF scanner app? I thought they thoroughly review apps in the App Store.
Or something.