>I still have zero clue what the hell they could have been thinking was good about the JVM.

Running one packaged program across every platform. Write once, run anywhere was Sun's slogan for Java. (Though oftentimes ended up being debug anywhere.) As for the slow start part, programs can either be often-launched short-running or seldom-launched forever-running. Assume because enterprise software falls to the later part (and runtime performance > startup time + memory use), focus was there.