Arguably the Cardinals have been playing a powder puff schedule up until this point of the season. Though no faulth of their own, their opponents are having poor years and this week they go up against a decent Steelers team, who as you'll hear all week in highlights, were without Ben Roethlisberger.
1) Running Game
This is the biggest factor the Cardinals lost the game.
I know Arians subscribes to using the passing game to set up the running game, but frankly it doesn't matter if you can't run the ball.