Pittsburgh has one of the best defenses in the NFL. Steelers coach Mike Tomlin realizes that. Because of skill position injuries to Ben Roethlisberger, James Conner and JuJu Smith-Schuster, the Steelers have a below offense. So Tomlin just doesn't want his quarterback to muck things up for the defense. That's why he made the switch to game manager, third-stringer Delvin Hodges. 
The Steelers are not a good road team. They've scored the second-fewest points on the road in the league. The Under is a perfect 10-0 during the Steelers' last 10 road matchups. So expect a very conservative game from them.
Kyler Murray could be hitting the rookie wall. He realies heavily on his mobility. That mobility is lessened, though, because he has a hamstring injury. The Cardinals haven't been helped by David Johnson's ineffectiveness either.