For one reason...his record as a winner:
"For his high school career, Martell went 43-0 as a starter, throwing for 7,507 yards with 113 touchdowns and nine interceptions. Martell also ran for 2,294 yards with 35 touchdowns. As a senior, Martell threw for 2,362 yards with 41 touchdowns and one interception. He also rushed for 1,257 yards and 21 touchdowns."
Practice is one thing, game time is a whole different atmosphere and some players shine on game day, others choke. If pretty looking counted Bernie would never have been tried at QB.