You may not see any of the behind-the-scenes costs that Apple has to pay for in supporting the ecosystem, but it is a well-known fact that Apple intentionally prices their software and services pretty close to cost, because they make their real profit on hardware sold and the software and services are just used to try to help drive hardware sales.
So, that 30% cost is really just the price of doing business in this ecosystem. It is entirely your choice as to whether or not you participate in this ecosystem.
That's wildly inaccurate. It's easily disprovable: Apple's costs aren't proportional to the pricing of software sold through it's stores. Does your refrigerator maker charge you as 30% premium on groceries stored in the fridge, or are there limitations on what groceries you can stock there?
The app store is wildly profitable, and Apple admits as much. While I have no objection to profits, we're all here discussing the issue because it's a tool used to unfairly thwart competition, impose monopolistic & unfair trade practices, which is why the EU and supreme Court, and possibly FTC are all involved in various complaints against Apple. If your fridge maker isn't allowed to regulate your groceries, Apple shouldn't be arbitrarily blocking and price gouging apps on their platform.
So, that 30% cost is really just the price of doing business in this ecosystem. It is entirely your choice as to whether or not you participate in this ecosystem.