I'm perfectly fine with JVMs, but at a guess, some of it is the usual snobbery for anything strange. But some of it is due to associating JVMs with enterprise nightmares. And some is that JVM tuning is a bit of a dark art. I've made some very good money going in and turning JVM knobs that others were afraid to touch. (The secret, by the way, is to hack together some decent load simulation and then measure not just median numbers but things like 99th percentile latency.)