We had this conversation while building our somewhat popular mobile game. Despite being a huge fan of Android, iOS remains significantly more profitable, especially in games.
By the most recent metrics I've seen, the top 200 iOS apps pull in $18 million a day, while the top 200 Google Play store apps pull in $12 million. iOS still leads (courtesy of the lubrication of things like iTunes gift cards -- there will again be a huge bump after Christmas), but is there any rational player who looks at those numbers and thinks "Oh, I want no part of the latter"? And note that this difference has been closing very quickly (iOS is up 20% YoY, Android is up 242% YoY).
Which is exactly why the majority of apps are built cross-platform from the outset. Whether using tooling that enables it easily (e.g. Unity, Titanium, etc), or designing around abstracting from the platform.