Strictly my opinion here, but Sims proved that when the team believes in you and plays on another level when the qb the team believes in is in the game you don't have to be the most talented player at qb. Especially when you have an OC who is willing to play to the offenses strengths as opposed to making the offense do things they just aren't that good at.
To be clear, I obviously am not the coach and I don't make the decisions on these things and will support whomever the coaches feel gives the team the best chance to win.