Scala may be written in functional style, which is a poor match for JVM (e.g.: uglyness of `@tailrec` annotations, absence of mutually-recursive functions, JVMs GCs are not usually optimized for that many ephemeral objects, etc).

Native code is not much better as a compilation target for FP, but at least you don't have to fight through JVM constraints first (GHC compiles to pretty efficient native code).