That's the entire problem. If a shopping mall was charging every store 30% of their revenue (not profit, revenue!), it would be very quickly going broke and empty. Yet Apple (and to a lesser degree Google, Facebook and a few others) is getting away with this - exactly because unlike the shopping mall, the developers don't have a choice. It is either play by Apple rules - or be excluded from a very sizeable part of the mobile market.
When Microsoft was playing dirty and abusing its market dominance to put a squeeze on companies trying to ship other than Microsoft's software, they got hammered in court pretty bad. The anti-monopoly/abuse of dominant market position laws are there for a reason, even if you, as a consumer, don't see it (yet).