In my experience, the juveniles who actually are incarcerated, beyond local detention, have seriously injured people. The system is designed to skew towards rehabilitation, and all but one of my juvenile clients have spent only a brief period detained, and were released to their parents/guardians pretty quickly.
The exception was horrific. I fought the transfer, and was able to delay it for almost a year. When his case was officially transferred he was 17, and he turned 18 before he pled (I didn't keep the case because he could afford me for the transfer, but became eligible for a court-appointed attorney once his case was transferred).
I'm a big proponent of better facilities and more rehabilitation services for people that need to be incarcerated. But from what I've seen, it takes quite a lot for juveniles, even in the most conservative counties of this state, to reach the point where that need arises.