I was looking back at my preview post. Goodness, a lot of my thoughts came true.
The game did indeed go lopsided for the Pack in the first half but the Steelers made their way back into it. The touchdown near the end of the first half was critical to Pittsburgh's chances.
Pittsburgh made critical mistakes, that often led to more mistakes. The pick-6 was set up by a bad penalty on a kick run back shoving the Steelers back from the 14 yard line to the 7. When Roethlisburger found himself under pressure at the goal line the options of taking a sack or heaving the ball were removed as they may have resulted in a safety by play or penalty. The Packers had 21 total points from turn overs during the game.
Even so, with three turnovers and untimely penalties, the Steelers had all the opportunity to drive down for the tying TD and winning extra point. It was clear that Roethlisburger was not playing well. They were disorganized and took too much time. They had lost their margin for error.
Green Bay took everything that Pittsburgh gave them. That is why they won this game.