Well, XCode is a great tool for building apps on iOS which a lot of developers already have, assuming they own a Mac. The tools for building apps for Android have only recently gotten better ever since Google decided to go with IntellijIDEA as their basis. I personally found it easier to build an app on iOS than for Android.
Note that this is anecdotal, and the stories I heard and read from other mobile developers are a couple of years old.
