He still spends two years from age 16-18 more or less in isolation in this treatment facility, where he won't be able to drink, drive, or see any of his friends. Plus, his parents are out nearly a million bucks, when it really does seem like they are root of the problem. Plus, he's still on probation until he's 26 so he has to be very careful afterwards or he's going to get a prison term anyway.
I'm not sure I buy their rationale as a legal defense, but the sentence isn't as light as it sounds.