I blame long drives that are so common here, poor road conditions, and the large proportion of elderly drivers.
Although they finished among the 10 states with the lowest occurrence of Careless Driving, Montana drivers were among the 10 worst in all of the remaining categories, dropping 8 positions from their previous 9th-place finish. Where did they go wrong? They maintained their #1 rank for Drunk Driving, and declined in the Failure to Obey category. You could also argue that improvements in other states were a contributing factor to Montana being at the wrong end of the spectrum.