Why doesn't the JVM cache JIT compiled code?

Oracle's JVM is indeed documented to do so -- quoting Oracle,

the compiler can take advantage of Oracle JVM's class resolution model to optionally persist compiled Java methods across database calls, sessions, or instances. Such persistence avoids the overhead of unnecessary recompilations across sessions or instances, when it is known that semantically the Java code has not changed.

I don't know why all sophisticated VM implementations don't offer similar options.

Without resorting to cut'n'paste of the link that @MYYN posted, I suspect this is because the optimisations that the JVM performs are not static, but rather dynamic, based on the data patterns as well as code patterns. It's likely that these data patterns will change during the application's lifetime, rendering the cached optimisations less than optimal.

So you'd need a mechanism to establish whether than saved optimisations were still optimal, at which point you might as well just re-optimise on the fly.

An updated to the existing answers - Java 8 has a JEP dedicated to solving this:

=> JEP 145: Cache Compiled Code. New link.

At a very high level, its stated goal is:

Save and reuse compiled native code from previous runs in order to improve the startup time of large Java applications.

Hope this helps.