There's a couple of reasons why Perl5 doesn't run on virtual machine X, be it Java or something else.

• Limited benefits. Perl is already extremely portable, and Perl can already access foreign libraries (XS, Inline::).

• Performance problems. Perl is highly optimised. Those optimisations would not be immediately available in a port.

• No formal specification. Perl is what perl runs. This and Perl's continual growth means that Perl is full of subtle behaviours and people rely on them. Each of these would need to be identified and replicated.

• Too much work needed. A good portion of Perl actually lives in modules, and those are often written in C. In Java's case, you could access Java's libraries instead, but writing Perl isn't the same thing as writing Java in Perl.

• Limited desire to spend the effort. For the above and other reasons, there is no interest in actually doing the work. For example, perlcc was finally dropped from Perl for being constantly out of date

That said, I believe work is actually under way for a Parrot port of Perl5. Don't quote me on that.

Update: I'd like to add a thought. We can discuss all the reasons for and against, but it really boils down to whether there exists someone who wants it enough to go out and do it. As far as I know, there is no such person for a Java port of Perl.