At the end, we were on our side of the field, and he was worried about us not dominating L'ville, and if he put in the backup, and a fumbled snap happens, suddently it isn't an 18 point victory, but maybe a 10 point victory, and an onside kick and a bad break or two away from a 3 point victory. I think Kelly think she can develop players during practice. I think he doesn't value junk time snaps.
He seems to require massive leads to play the backup QB, and we rarely have massive leads.