Many players have commented on how surprisingly difficult it is to switch sides on the OL. Every instinct the player has must be reversed. After 4 years of playing LT, I could see changing over to RT being a real challenge.
My understanding was that coaches were beginning to realize this and, to make rookie adjustment easier, just keep players at their college position whenever possible if they were expected to start immediately.
If he's going to be a backup / learn on the bench his first year, the coaches can then be more flexible about shifting players around to different positions.