Apple has announced it has paid out $70bn to developers in the nine years since the App Store ;aunched with the iPhone 3G. Allowing for some variance in the commission Apple takes on differenrt payment types, that equates to a total spend by Apple's iOS customers of $100bn.
For a service Apple was originally not keen to launch that's a hugely impressive accomplishment.
It's the size of this pot and the willingness of iOS customers to pay for the apps they want which keeps developers focused on the App Store. Whilst Google has made great strides towards deliverng a similar service in the Play Store, the truth is that the larger number of Android customers don't translate to similarly large numbers of app sales.
Whether that's because Android phones are more likely to pack the apps users want from the start or because Android phones are generally bought on value - and therefore at the cheaper end of the market is up for discussion.
The end result is the same. If you want to create a viable business as an app developer, you need to be developing for iOS.
It would be interesting to compare the success of the iOS App Store with sales across Macintosh for the last thirty-plus years. My guess is that developers have gained more income on iOS than Mac in around a quarter of the time.