I think in the case of Apple it's more difficult to challenge due to the existence of Android. iOS doesn't even have 50% of the market mobile OS market share globally. You can argue Apple has a monopoly on their own products, but then we'd need to also discuss the same for Xbox, Playstation, Nintendo, and any other device that has its own marketplace.
I'm not sure about the stats on gaming consoles, but Apple has over 50% marketshare in the US last I checked, and we're talking about US law here so US marketshare is really more important than how many Android phones people in India and China have. So having a majority of the market which almost everyone these days buys from (almost everyone has a smartphone now, not like gaming consoles which are a niche market), and then forcing everyone with an iDevice to use the Apple App store, is a clear monopoly unlike some gaming console that a small single-digit percentage of the population (or less) owns, and competes with 2 other big competitors, is not the same.
It is not just about AppStore fees but also about the fact that you are forbidden to use any other store to buy/download apps from and you are forbidden use any 3rd-partty payment processor for payments inside your app. They force you to use their systems with 30% cut. That feels anti-competitive quite a lot!
