This is due mostly in part to a lack of a goalline short yardage back, and lack of creativity. Either find a bulldozer at RB, or run Allen. I believe Hurts led the NFL in short yardage rushing TDs last year, and far fewer of Allen's 15 rushing TDs came from 1-2 yards or in. That also speaks to a lack of push from the OL.
#1 - lack of elite short yardage / goal-line back
#2 - lack of OL push
#3 - lack of creativity from OC - think KC's shuffle passes to Kelce.