After all, it's their house so their rules...
Apple have carved out a significant market share of mobile users. They've locked down the OS so you can't install your own apps on it and they've crippled the browser so you can't build nice web apps. For businesses like Netflix, Spotify and Epic who's userbases arguably transcend the App Store, why should they pay the Apple Tax?
Apple doesn't "own" these users. But if you want to extend your services to them you have to pony up.
The iOS operating system, developer tools, platform libraries and the App Store and distribution system are all Apple products built by them on their own dime and at their own commercial risk. On what basis do you get to dictate to them what features they must or must not develop, what services they must be coerced to provide and what contractual relationships they are required to enter into? There's just no basis for that.
Apple has a monopoly on how those products are sold and licensed because they are Apple products, in exactly the same way that Fortnite and it's marketplace are Epic products. There's no requirement for Epic to open that up, and if they do it will be on their terms. Their house, their rules.