At first I thought this sentence was disastrously short, but the judge's reasoning does make sense. The guy confessed, was open/honest about his crimes in court and was intent on rehabilitation--that's the perfect formula for lenient sentencing. Had he been apprehended after a long search, pleaded Not Guilty, behaved badly in court, showed no remorse and gave no indication of ever changing---then he probably would have been locked up as long as the crime warrants.
Throwing the book at him could have resulted in a 'cruel and unusual punishment' case in an Appeal (possibly resulting in being freed even earlier than the lightest of sentences) and would have set a precedent that actively discourages anybody else for ever coming forward. With that in mind, I think the judge made the right call.
