Shaun_Max Whenever I have looked at it Apple's app store is larger in terms of revenue than Google's.
At the same time the Android ecosystem is far more diverse by pretty much any metric, including screen size (and shape, and pixel shape, and colour), performance, OS version, features available. So it is much harder and more expensive to cover all possible devices.
I know there are other app markets for Android devices, but they are all small and involve additional effort to target.