If you remember the first versions of the App Store, most of the apps were hosted and delivered by Apple, and the in app purchases were also hosted, secured and delivered by Apple. You just uploaded the content and had zero cost from that point on - like writing a book and giving it to a publisher. There the 30% cut made sense. If I sleep on the beach all day and receive 70% royalties for my stuff without having to do any other work, great. Sounds reasonable.
Not so if I’m running a service or a backend for the app I’m selling. If I’m selling consultations, or running perpetual servers or jobs or bandwidth for each new sale, there’s absolutely no way 30% is a sensible cut, because the value is not being provided by Apple the publisher.
Apple has failed to make this distinction, and the more they dig their heels in and refuse to, the bigger the fall is going to be.