UB-freeness is not a goal in-and-of-itself. It's shorthand for a certain kind of technical (i.e. non-functional) correctness, which, in turn, is related in some ways to functional correctness, and it's improving functional correctness (and I include security here) that's the goal. Is the most effective way to achieve that is by working to completely eliminate undefined behavior? I'm not at all sure.
Isn't having a UB-free JVM a noteworthy goal though? Especially if it gets used in life-critical systems such as avionics or autonomous cars.