I think there must be many young people here :)
In the old days, you *paid* for OS updates. If you didn't, your computing device got progressively harder and harder to keep going. You often *had* to pay for the OS update *in order to* use the latest software. Even now in the Android world, unless you're using vanilla Android then you're playing roulette as far as receiving support is concerned.
Today, I can install iOS 13.7 on an iPhone 6S, a device released 5 years ago. Not only can I install it; unlike in the bad old days, it will run (like-for-like software) at least as fast, and in some cases faster, than the original iOS 9 it shipped with.
I do not want to go back to the old days. I'm very happy that the markup I pay for App Store purchases goes to fund the continuing development of the OS and its support on older platforms. It keeps my hardware fresher for longer; it keeps my hardware more valuable for longer; it allows me to keep on buying apps from developers via the App Store for longer.
By doing this, Apple *more than* justifies its mark-up; by doing this, Apple ensures there's a tremendous (and unfragmented) market for app developers, which in turn allows app developers to prosper.
Let's not forget that the App Store itself was an innovation.
It is not a coincidence that app developers (as a whole) make *far* more money on Apple. Sadly, however, that last may be their undoing; if developers make more money on iOS than on Android, perhaps that shifts the balance in terms of market position and anti-competitiveness? If it does, however, it will be IMHO a very sad day, since the model will have proved itself so good as to be destroyed!