Are you serious? robustness, performance and productivity of the JVM?
Better garbage collection, threading support and long-lived processes support was mentionned by the twitter engineers as advantages of the JVM over Ruby. Both Python and Ruby use a Global Interpreter Lock so multicore concurrency is basically impossible.
Not sure how you arrive to the conclusion that Java is "not performant at all": it compiles to optimized code near what good C++ compilers achieve;, it has a highly efficient, state-of-the-art garbage collector, native threads, little object overhead (at least compared to dynamic languages). The Hotspot JVM is a state-of-the-art runtime that makes even .NET look silly in places. Perhaps you were using a slow library; the language itself is certainly among the most performant available.
With mobile devices running on limited power, efficiency gets more important today than ever. The runtime overhead of dynamic languages is something that will put software using them at a disadvantage.