I think multiple implementations is more or less a C/C++ thing. If you look at other platforms (Ruby, Python, PHP, Haskell, Java, Go, Rust, Scala, Lua, Perl) there's basically _the_ version and maybe some ancillary implementations.

In fairness, it's hard enough to build a language people use that solves real problems. Asking someone to do it more than once, or to do it once but create specific enough documentation and tests so someone else can also do it -- and then get someone else to do it -- is practically impossible.