[chubot]

I would say it's:

1) There's a large difference between a compiler that exists and an efficient one. The JVM is designed for Java and not C, which makes efficient compilation hard / impossible. Graal as mentioned is an extremely unusual research technique that may make it feasible.

This comment is related:

https://news.ycombinator.com/item?id=19065829

Basically people underestimate how hard it is to make a VM that can run multiple languages. JRuby and Jython work, but it takes heroic efforts.

2) The interface to the OS, as mentioned. You can maybe run some algorithms like image processing, but try running the native sqlite code on the JVM, or something even hairier involving networking. It's not straightforward.

WASI provides something that's closer to what C programs expect than what Java provides. As I said, the market voted with its feet. All the friction adds up. If you try hacking on that compiler or manually porting code, you'll probably get a sense of why that is.