Amenable to Treatment?

I've made various references to juvenile law cases in the news -- and here I make yet another. A 14-year old boy murdered his step mother, his 13-year old step sister and his father. The news stories present that the choices of "treatment" are either commitment until age 21 or inprisonment in adult prison for up to 50 years.

It is not clear to me why there has to be such a dichotomy -- why there needs to be either "juvenile" punishments or adult punishments. The juvenile justice system was initially put into place to ensure that young offenders are not subject to adult punishments (fueld by the hanging of a boy less than 10 for a murder). Since the creation of the juvenile justice system due process rights (or many of them) were awarded to youths (via In re Gault) and debate intensified about if youths with adult rights get adult punishments.

The juvenile justice system is in place -- still with the intent to help rehabilitate rather than punish youthful offenders -- then, why is it that the choices are either results that seem inadequate or adult trials that will most likely be too harsh? Why can't this young man, somehow, fit into the legal system in a way that fits his crime?