What effort? One of Epic's main arguments is that they want to distribute their iOS app without using Apple's services, but they can't because of artificial restrictions that Apple has implemented inside a product that, once sold to the customer who is Epic's target for the app, no longer belongs to them.
The effort to build into iOS the APIs needed for Epic's games. The effort to document those APIs and host developer conferences where actual iOS devs give instruction on how to use them. Do you see any first-party iOS games that look anything like what Epic sells? I sure don't.
If it is seriously costing them serious money to maintain the current state of their documentation then something is seriously wrong.
I think the 30% cut is ridiculous but it's a give and take for both companies.
But it's not like Epic is selling that, or asking Apple to allow them to have their own manufacturing plant for iPhones, is it?
The iPhone is an instruction-executing machine. That's what people buy. Epic wants to offer a specific set of instructions that people who already use the iPhone can execute. Why should Epic have to go through Apple to do it, if there's nothing in that machine that would prevent Epic from doing it on their own, besides artificial limitations which only have that specific purpose?
That's not what people buy; that's the hardware they receive as part of their purchase.