The Java programming language is only part of the story. There is also this thing called the Java Platform, aka the JVM. You can't just simply switch to Scala, your Scala code needs to be executed by something.
http://www.scala-lang.org/node/168
Yes, I am aware of the problems of this, too. * Not as stable as the Java backend ever was * Any code that used Java libraries explicitly needs to be rewritten * Stallman is going to throw a hissy fit about it being .NET