Because the Ravens and Steelers split the two games they played against each by the same winning margin of three points, a tie-breaker would have to settle it. The only problem with that is the Steelers could have went for a score on their last drive instead of kneeling down three times and owned the tie-breaker.
They had almost two minutes left and were on their own 46 yard line. If they would have tried to get another 20 yards they could have tried a field goal and had a six point margin of victory. This would have given them the head to head tie-breaker, which is the first tie-breaker in the NFL, over the Ravens. But they were content to just win the game and helped the Ravens be in the driver's seat for the wild card. This was probably a coaching decision
I'm not sure what other tie-breakers some of the other teams involved in the wild card chase would have over the Steelers, but at least we would be ahead of Baltimore. Watch the Steelers vs Ravens video highlights and check it out for yourself.