eg want to run code for 6 months at a go managing hundreds of gigs of data, tens of thousands of threads, at high load, with sustained gigs a second of garbage generation? the jvm will just silently tick away doing just that while being nearly bulletproof. As much as I love ruby and python, you ain't doing that with them.

With hot code loading, introspection, etc. All the stuff that makes developing super-robust long-lived systems way easier.

And the flip side of the clunky language is your code from 20 years ago still works.