One rationalization is that a 10 year probation means he'll be under police watch for a significant amount of time. On the other hand if he was given a sentenc

One rationalization is that a 10 year probation means he'll be under police watch for a significant amount of time. On the other hand if he was given a sentence as a minor, he would be released in 2 years when he's 18. That leads to the question why he wasn't tried as an adult, but IANAL.