The whole point is Apple is providing next to nothing for those digital "goods". They aren't providing the digital content. They aren't providing the backend that provides those services. Many of those systems exist fully outside of the Apple and Google ecosystems on the web, so they already have their payment infrastructure in place. Just one side charges 3%, and the other side demands you use their system and oh by the way, pay us 30% for delivering no value add.
You want to charge developers for making software, do it up front. Increase your developer fees. On the bright side, maybe it will eliminate a lot of crap that is making the app store bloated.
On the other hand, maybe they shouldn't actually charge developers anything. My argument is the iPhone would have been nothing without developers. A lot of the big developers on mobile were on desktop or web long before iOS (Yeah, thats probably changed a bit as we've hit the 15 year mark, its not all the old guard of developers anymore) ... they didn't need Apple to invent the iPhone. Did it help them? Sure, but Apple would be no where without their apps. They would be a company with dwindling PC market share, stuck on Intel, probably no phone market share having been replaced by more open platforms, and the iPod would have died out. Everyone knows the exploding iPhone business made Apple what it is today.
The original iPhone without app support sold okay, but it was nothing close to the success they saw after creating the App store. Apps add value to the platform, they make people want to buy the hardware. So IMHO don't nickel and dime your developers and focus on making the OS and hardware the best it can be. You are already making more than enough in that business to pay for all of its development - especially Apple with the highest margins in the industry. All of that R&D that people around here claims goes into the tools needs to happen regardless because they are used to make the system.