Pretty sure you can buy from Steam on the iOS app - Steam just has a revenue-sharing agreement with Apple.
which is specifically the part that got Epic in trouble, they don't want to share revenue with Apple, and what's more they want to charge other developers a fee for the use of Epic's app store.
the thought that Apple was just going to let this hilarious ToS breach lay was all wrong, absolutely not
Re:Apple, Epic, and the App Store
by ThatPlayer on Monday August 17, 2020 @08:54PM
(#24194146)
Steam Link on iOS actually has to run a version of Steam Big Picture without a Store or Community option because of Apple's rules: https://arstechnica.com/gaming/2019/05/apple-reversal-allows...
The Store application lets you buy games because you cannot consume them on the device, like how Amazon allows you to buy physical items but not Kindle books.
If you were trying to remove the monopoly, I'd think you should start there, and then expand to other people who can prove they have their shit together. Epic let someone else use my email address to sign up for an account (and they only allow one account per email). That is serious amateur-hour territory. When they have figured out how to tie their own shoes we can talk about whether they should be in the running.