Because there is so much hardware variation in the android world, it is difficult to provide any kind of consistency across experience. It is very easy to program for Apple hardware is 100% consistent across them, any given generation. Android, in contrast, has wildly varying hardware specs.
There's also a fairly well-known problem across developers that the android marketplace is basically Mos Eisley. Piracy is rampant, commonly available to even standard, locked android phones, and Google is doing nothing to correct the marketplace of the design flaws which allow this to happen every day. For many developers, developing on android is simply not a priority because they will not see money for it.
Edit: Joe, with the conciseness.