Any given language can be compiled into Java bytecode if you write a compiler that does it. There is no arcane barrier that prevents you from writing a compiler for compiling C, C++, Common Lisp, Scheme, Haskell, Prolog, Forth or any other arbitrary language into JVM bytecode – there is no need to use a detour over a compiler that first compiles into Java. It's probably about as hard as writing a compiler which compiles any of these languages into x86 or x86_64 or whatever other assembly.
Yes, there aren't compilers for all languages into Java bytecode. Just as there aren't compilers for every language into C or Assembly. That doesn't tell you anything about the language, though.
What a language compiles (translates) into is not a property of the language but of the compiler used. If a given compiler does not exist, you can write it.