MP machines are not rare in corporate projects -- it has been many, many years that I've worked on a project that didn't run on MP servers.
One of the big reasons that decision makers like Java is that it is true that a little extra money can boost performance of a well-threaded program. Whether you agree or not, this is what is commonly believed and past experience does seem to bear this out for me.
Also note that it is usually easier to design failsafe features into a monolithic program than a grid design. Most of the problems I encounter on my current project are due to failure handling between the multiple applications (~7 programs for one "app"). We have one large open source project saying threads are for weenies (Python, GVR) and another saying monolithic is the only way to go (Linux kernel, LT). Discounting the performance argument, what other design arguments have been made in favor of the Linux kernel over Minix, etc.
Jython, however, was used in one project to great success, but there is a feeling among management that it is not a "real" project and it may fall by the wayside.