In Java, there are multiple languages that compile to Java bytecode and can run on the JVM -- Clojure, Groovy, and Scala being the main ones I can remember off the top of my head.

However, Python also turns into bytecode (.pyc files) before being run by the Python interpreter.  I might just be ignorant, but why aren't there any other programming languages that compile to python bytecode?  

Is it just because nobody bothered to, or is there some kind of inherent restriction or barrier in place that makes doing so difficult?

Simple - last time I checked, Python had no formal specification, including its bytecode. CPython is the spec, and bytecode portability is IIRC not required. Thus, it's a moving, undocumented target designed for a specific language.