Since I'm considering trying my hand at mobile development, I've read up a bunch on the topic. To vastly oversimplify the issues, the biggest problem is that there are so many different kinds of Android devices that it's more like developing for the PC. The iOS ecosystem is gaining more and more variants, but for the most part it's like developing for consoles where you have a set number of device types to account for.
Another big aspect is that Android users seem much more reluctant to part with their money. For whatever reason, paid apps don't sell nearly as well (generally) on Android than they do on iOS.
it also creates something of a negative feedback loop. when android users see ports of games from ios that come off as buggy it makes us a little less likely to buy another.
I do think that piracy is a much bigger problem facing android though as it's incredibly easy to share games.