I would say the most disappointed fan base on Sunday would have to be that of the Miami Dolphins, by far.
With two weeks ago all they needed to do was beat either the Bills or the Jets, and they're in the playoffs. The 2013 season was a nauseous roller coaster ride, from the euphoria of winning the March Super Bowl (aka Free Agency), being given more hope from national media based on the Patriots' situation at TE and WR, then a strong start to the season (two road wins in weeks one and two).
That was followed by a four-game losing streak and the Incognito-Martin story and then things looked good with a three-game winning streak to vault into what looked like an excellent chance to make the playoffs, as they had an 8-6 record. One (or should I say two) final roller coaster dips: shutout by the Bills, and a home loss to the Jets; being outscored 39-7 in the final two games by two teams with losing records.
For the three teams in the poll, expectations on Sunday were low for Dallas fans based in part due to the week 17 results the last few years, and the knowledge Romo was not playing; Steeler fans probably weren't expecting much because they needed so much to happen and probably assumed they would miss the playoffs long ago; Bear fans saw so many players on their defense sidelined with injuries they probably figured that even if they did win, they would go one-and-done.