Cons syntax, powerful functional support and next-level coroutines for multi-tasking. Kotlin allows you to more concisely say what you want the machine to do, and write it in a form that that the machine can efficiently perform. I suspect the reason it was chosen for Android is that for an event-based system--particularly one in which you need to be careful about which thread you are on--then Kotlin is an excellent choice.
Thanks for the question.
Head First Android Development