Riley Burt is a very talented RB that ran using his instincts.  If the hole wasn't there in the line, Burt would bounce the ball to the outside to gain yards or score(ie HAWAII game). Good running backs do this all the time but I think there were coaches who were very strict in their style of play which left little room for the RB to do anything on his own.

Also, I think LITTLE LEAGUE politics may have had something to do with who played which is unusual at the COLLEGE level.  BYU also started using smaller RB which for BYU was a big change in direction.  Most of the RB's that have done well at BYU have all been at least 5 - 11.  Unless you can find a WALTER PAYTON or BARRY SANDERS, smaller running backs are at a real disadvantage.  The same can be true of RB that are bigger but are too slow.

BYU used to run a lot of SWEEP running plays because they struggle with the straight up the gut running and the staff in recent years have been trying to improve the OFFENSE blocking technique on RUN plays.