Steam does not sell iOS software. They sell games for Mac, Windows and Linux which you can buy also directly or at a competitor such as GOG, if the developer chooses to.
To sell into the iOS ecosystem as a Dev you can only do it via Apple so far. Epic wants to sell their own iOS multiplayer games and in app lootboxes without forking 30% to Apple.
I do wonder: anybody knows if Amazon pays Apple for the things I buy through their iOS app?
