My favorite game on Android isn't on iOS yet. THAT bugs me!
There's actually a few novelties I have that aren't on iOS.
I don't think the popularity of the phone is the problem, the majority of iOS games are not made for the iPhone, but rather the iPod Touch. They run on both, but you can get that if a kid is using their parent's iPhone to play a game too often, that they're most likely going to invest in an iPod for them. Most are unaware that there are Galaxy Players, and only think you can an Android non-smartphone in tablet form.
Some engines work better than others (each vary on what they support and you can't switch just for the sake of it). And when it comes to things like Unity, which a lot use, it's an extra $400-$1,500 investment just to develop for Android.