simple - he has no arm so he must be starting because he is mobile. What other reason could there be? (the commentators can't say that coach Flood is a meathead)
They've been calling him mobile all season. We've seen maybe 2-3 scrambled in the last 2 games. His mobility is either greatly exaggerated or not being used.
I still say Rutgers is feeding the announcers this narrative. Rettig hasn't played enough for someone to watch the games and say he isn't mobile -- especially since Rettig looked mobile enough in his only full half of football. So, the announcers aren't getting this idea on their own.