It is perceived to be a depth problem at that position. Long ago it was unthinkable to start a first year player. Even back when freshmen were ineligible and first year players were sophomores.
Vince Dooley, for example, had no intention of even playing Herschell Walker in 1980 when he was a freshman, much less starting him in any games. Got behind 0-15 to ut in the opener and said what the heck. Put him in and Walker ran all over them. Walker started every game after that as UGA went undefeated and won the NC. Herschell finished third in the Heisman voting in 1980, and to my knowledge, was the first freshman to ever finish in the top 10. Was probably the first one to ever even get a vote.