There are a few blatantly obvious reasons why oracle would do this:
  • To advertise the jvm as a viable scripting virtual machine. All scripting engines have some sort of virtual machine, but the jvm is more advanced than most others (if not all).
  • JavaFX includes a complete webkit based web widget with javascript, so they need one. It's using the webkit one now afaik but obviously it would make much sense to use a single vm.
  • Add to the java "eco-system" with another tool for use by developers and integrators: e.g. as an extension language, or simply as another execution platform for alternative languages.