Scala compiles too slowly. Otherwise, it would be more popular. In general, I think it's a bad idea to make these sort of excuses. Java as a language needs to better compete. The Perl community, for example, used to diss Python by saying CPAN gave it a huge advantage. Perl lost momentum and all the kids now use Python. C# can be used with Unity, for instance. Gateway drug. :-).
> Scala compiles too slowly. Otherwise, it would be more popular.
For day-to-day Scala development incremental compilation etc. mean that a typical build in my IDE takes about a second. I think it has more to do with Java being the default/official language for the JVM (and the Scala learning curve). Similarly, F# is a great language, but C# has always been seen as the default go-to language for the CLR (VB.NET anyone?).
Scala 2.10 compiles our ~150 file project (which has some seriously big files with lot of implicits in them) in about 15-20 seconds for me. Incremental compile times are typically 1-5 seconds. And this all on a laptop from early 2011. Indeed, this is slower than Java or C#, but nothing terrible. Running any test suite takes much longer.