That's part of it, but it's also just that there's little motivation for using it as a general-purpose VM. Building a precise clone of Python on the Erlang VM would be more difficult than on JVM, but more importantly, it would be pointless — Python does not have the kind of deep-rooted concurrency semantics that are Erlang's raison d'etre. If you try to stick an existing language that doesn't closely resemble Erlang on the Erlang VM, all you're doing is creating a really awkward implementation of that language and not really gaining anything. So you end up with languages that are similar to X but with a huge transfusion of Erlang's semantics so that they're useful.