[OtinG]

Apple does not write the apps like FBReader Plus. The people who created FBReader Plus write the apps for the various platforms. Try writing to the creators of FBReader Plus to see if they will write an iOS version of the app. They will likely turn their noses up to you. But again, that is not Apple's fault, that is squarely the choice the FBReader Plus creator has made. Again, it is the creator of FBReader Plus who is short selling her/his app by not making it available on iOS as well as Android, it is not Apple's fault.

The smart app makers write app versions for both Android and iOS. Some just write a single version for one or the other. No one can control that except the app creator who makes that choice.

ETA: Many app developers stay away from iOS because they don't like the security rules. That is their problem, not Apple's. I personally prefer the strict security rules on iOS. It makes using the iThingies way more safe and secure than any Android device will ever be. Android is written by Google, and Google has made it clear through repeated actions over many years that they don't give a darn about our security nor protecting our personal data and information. As a matter of fact, they love data mining and selling our info to the highest bidders. Give me a garden wall any day over total chaos.