Because walled gardens aren't illegal? Epic is trying to argue that a product and ecosystem setting it's service costs is somehow a monopoly of that type of service despite clear indication it is not. Apple is the defined innovator of smartphones and app store, however they are not the only one who is able to offer such a product/ecosystem. This is Epic's main argument and it didn't stick because it's correlated to the actual real world where they are not monopolistic, thankfully a clear point the judge made in the hearing.
There are also huge ramifications related to the industry that can come from a haphazard ruling, and considering Epic's arguments presented, they definitely don't give a shit. Trying to claim 71 million people are out of luck right now is disingenuous due to the fact those same 71 million can easily access alternative measures for playing, Apple is holding a gun to their head saying play on ios. There is no case here from Epic, in part due to the pied piper actions of Tim Sweeney (who has clearly fucked the case up due to his public outcries), but also because they are trying to claim monopolistic behaviours while also they themselves displaying such attitudes.
On top of that, Epic's display of stupidity in breaching the contract intentionally with clearly defined marketing schemes organised many weeks in advance is working against them. They even state that in order to work against an entity you don't agree with you have to prepare, which means they had the intention to breach contract, a big no no in legal world. They have no argument basis there and even try to use the concerts as proof of users missing out on Apple's choice to ban Fortnite.
Epic's flagrant disregard for laws or attempts to brute force their own interests into others is just becoming more and more apparent as time goes on. They want to leech of other's ecosystems and break down their perfectly permissible walled gardens, all while asking the owner to pay for their use of the walled garden. 30% is a high amount, and that can be argued for reducing, however that is not the approach Epic went with, instead landing flat on their face in a sorry attempt for "monopoly" shenanigans.