Are you fine with paying Apple 30% of the cost of any application that you buy? It's not the developers that are paying this cost -- this is what you are paying to Apple for each app. That $25 app is costing you $7.50 that goes straight to Apple. All that money adds up fast.
Even if you are good with that, I think you imagine that a lot of users -- even those who might be happy with other aspects of the Apple ecosystem -- might not be happy with a 30% tax on all purchases made on their thousand dollar device. Apple even mandates that you're not allowed to know inside of an app about cheaper ways to pay.