Making an app available on Android generally doesn't double the revenue they were making on iOS. There have been a number of iPhone apps that have ported to Android and found that their support costs go up but they don't make nearly as much revenue. There are certainly exceptions but they tend to be big apps that can get a lots of views of ads, like Angry Birds.
Porting from iOS to Android is far from trivial. Plus Android users will post bad reviews for apps that look too much like iOS. So you have to redo half of the graphics and some of the UX unless it's a game. At that point, it takes nearly as much work to do the Android "port" as the original version.
I don't have the time to keep up with 2 platforms in depth and, personally, I just don't like Java or the tools. It'd take something far more compelling that lots of eyeballs (without lots of dollars) to make the effort for Android.