Which I think strikes right at the point here. This is practiced throughout the world and throughout industries, but for some reason we think it should be different for mobile phones. I don't see why it should be, especially given that in the overall market, Epic can publish their game across multiple competing platforms: Android, Windows, macOS, Linux, Xbox, PlayStation, Switch, etc. and iOS until recently.
In fact, as you mentioned, if you don't like the Apple Store you can go to: Steam, itch.io, GOG, or host a website yourself. If I can't create an arbitrary game and have access to Epic's user base, I don't see how it's different. Can I use Epic accounts on my own indy game?
I think you are narrowly defining the marketplace as being only iOS, when in fact it's much larger, and you're not taking into account that this is all about access to users. In both of these areas, it's hard to find compelling activity for Epic. They can and do publish Fortnite on multiple platforms, and they also arbitrarily restrict access to their own user-base.
Epic just wants to have their cake and eat it too and I have yet to see compelling evidence to the contrary, myself.