Epic needs payment processing and licensing.
Fortnite really doesn't need to be promoted by Apple on the App Store and what not - let alone at a 30% commission on all transactions. It's popular enough on its own. So is Spotify or Netflix. If anything, Apple are providing services that Epic neither wants nor requires (considering the commission rate).
That's a mere presumption. Well-known and popular as they are, it's not as if Epic's games aren't competing with other developers' offerings on the App Store. Once you remove the glass floor of Apple's commissions, prices can still decrease.
They could technically - though obviously not overnight, without considerable damage to the ecosystem and users. But the disruption isn't any higher than a change of operating system (OS9 > OS X) or processor architecture (32bit > 64bit, or x64 > ARM), if access is phased out over a certain transitional period of time. And users are still free to use legacy system to run their apps.
One indication is the fact that they don't provide the same security on other platforms (macOS) - even though people store sensitive data or make financial transactions that are just as high-value or more on Macs as they do on iPhones.
Another is that Apple has been
caught to make up and bend its own rules to disallow certain apps - for purely anticompetitive motives:
https://www.theverge.com/2020/8/6/2...le-stadia-ios-app-store-guidelines-violations
https://www.theverge.com/2020/9/18/...ming-xcloud-stadia-app-store-guidelines-rules
There is no justification from a security or privacy standpoint to disallow game streaming service apps. Heck, if you're purportedly so concerned about security, forcing developers to make every streamed game into a separate app makes the environment
less secure. Neither is there any justification from a content perspective. Does Apple review every song streamed by Spotify, book offered by Kindle or film streamed by Netflix. They don't.
Lastly, my opinion that gatekeepers unfairly exploit their position for their own gain - and that includes pricing - is shared by European lawmakers. It is implied as reason for drafting this law (the Digital Markets Act).