Why is that? Tooling support at this point is much better for Scala than it is for many JVM languages, including Xtend.

Checkout: https://github.com/pocorall/scaloid

You can do that in combination with IntelliJ IDEA for example, which has awesome support for both Scala and Android. Google's new Android Studio is actually the same as IntelliJ Android plugin that they distribute as part of their open-source distribution. It's also the best IDE ever.