I could say exactly the same for any source-to-C compiler, and/or any system allowing decent FFI with C. Unless there is some different reason than the JVM itself, C has an even larger code base.
In a way, C can be considered an "existing platform" in much the same sense. I didn't include it in my list of examples because I really don't want to have to fight build tooling and cross-platform dependency hell in 2012 if I don't absolutely have to. With e.g. the JVM, you can get a jar from somewhere (or maven it in), and -poof- it just works, everywhere. This is a major advantage to the whole "ecosystem" point.