The JVM doesn't run on Android or iOS, and never will. That's a huge chunk of users they can't touch, but the web can.

Aren't all Android apps running the JVM?

They run Dalvik, which is Googles proprietary VM. Its similar to the JVM in purpose, but it is supposed to avoid Oracle's patents and has a few specializations for mobile.

AFAIK (I'm not a java developer), any language that can target the JVM can target Dalvik.

AFAIK, the only language that's officially supported by Dalvik is Java, and code in other languages tends to run into limitations in the bytecode-to-Dalvik translator.

Surely there is a Scala for it? Alternatively use Mono and C#/F#.