What if the payment is for something other than just the game or app? What if the app is part of a broader ecosystem that includes videos and merchandise (for example)?
There are numerous exceptions, which is how Amazon, Uber Eats, etc get away with bypassing the App Store payments (because they are providing physical goods). If an app is only unlocking content, even if that content is spread across other platforms, then it needs to use in app purchases. (And you enter a world of hurt as you try to sync a users subscription or purchases across all platforms)
