Epic Games has for several years now been engaged in a legal war with Apple and Google, centered around the closed ecosystems of iOS and Android: Where developers have no choice but to pay a 30% store fee on all revenue. The massive success of Fortnite seems to have brought this into sharp relief for Epic and CEO Tim Sweeney, who argue that it should be able to distribute its games on these ecosystems without paying just under a third of its profits to the gatekeepers.
So far it's spent an awful lot of money but had mixed results, with Fortnite still unavailable for iOS in the US. Epic has reached a stage where the Epic Games Store is available on Android worldwide and on iOS in the European Union, and it's now taking the next step of distributing games through that storefront (it takes a 12% cut of payments it processes, but 0% of payments the developer processes themselves). As part of this Epic is swallowing the cost of Apple's Core Technology Fee, which it calls "illegal", for participating developers.
This is a step forward, of course, but it's not any kind of long-term solution: The vast majority of customers are always going to prefer the direct convenience of the App Store or Play Store. Epic's fighting an uphill battle to even get developers to use the EGS on mobile, but that in itself will no doubt be part of its ongoing legal arguments with the platform-holders.