Sure, but if the community got sick of Epic's walled fortnite garden, they can play other games. Could be WoW, could be Call of Duty, could be Pubg, could be the latest Mario. It doesn't really matter. Fortnite competes for your time with all other games, and the main thing keeping people there, besides basic enjoyment of the game, is that a lot of people play with their friends. And not many people will say that certain in app purchases are essential item (unlike, say, having an email app on your phone).
iOS on the other hand has a single serious competitor, Android, and if you have an iPhone you can't install Android on it when you get mad at Apple - you need a whole new phone. From a developer's perspective, you would miss out on all the iPhone users if you ship and Android app and not an iOS one. In that sense, Apple has significant monopoly-like power over the app market; solidified by the fact that you can't just install Google play store and start downloading Android apps on your iPhone if you get fed up with Apple' App store. The switching costs are too high for most users to consider it, except when buying a new phone.
A lot of this comes down to what a meaningful market is. E.g. Border's and Barnes and Noble learned the hard way that they were in the same market as online book selling - you couldn't usefully look at their book store models and ignore Amazon in the last ~decade.
iOS on the other hand has a single serious competitor, Android, and if you have an iPhone you can't install Android on it when you get mad at Apple - you need a whole new phone. From a developer's perspective, you would miss out on all the iPhone users if you ship and Android app and not an iOS one. In that sense, Apple has significant monopoly-like power over the app market; solidified by the fact that you can't just install Google play store and start downloading Android apps on your iPhone if you get fed up with Apple' App store. The switching costs are too high for most users to consider it, except when buying a new phone.
A lot of this comes down to what a meaningful market is. E.g. Border's and Barnes and Noble learned the hard way that they were in the same market as online book selling - you couldn't usefully look at their book store models and ignore Amazon in the last ~decade.