We realize that the Cardinals won the NFC West relatively early in the season. However, suspicion boomed after the Cardinals lost four of their last six games, all allowing 35 points or more in each loss. Even more so, three of their four losses were against NFC teams that made the playoffs (Eagles, Vikings, Giants) with both wins coming against opponents with a combined 6-26 record (Rams and Seahawks). The one thing going for them is their 6-2 record at home, with wins against the Dolphins, Bills, Cowboys, 49ers, Rams and Seahawks.
The Falcons, on the other hand, finished their unbelievable season with a three-game winning streak, winning seven of their final nine games. Victories during that stretch include at San Diego, against #2 seed the Carolina Panthers and the Minnesota Vikings. Their 13-10 win during the Buccaneers implosion, eventually forced Tampa Bay out of the playoffs; suffering a four-game losing streak. Combined with Michael Turner (1,699 yards rushing and 17 touchdowns) and Matt Ryan (Offensive rookie of the year), the Falcons finished with the league's sixth best offense. However, the Falcons finished 3-2 against playoff teams, and only a 4-4 record on the road.
Being only two-point Vegas favorites, the Falcons are overwhelming favorites by most analysts. Even though they secured early-season wins against the Miami Dolphins and Dallas Cowboys, the Cardinals only went 1-4 against playoff teams. Their early season surge was impressive, clearly dying after going an unimpressive 4-4.
A full body of work is good and all. But you have to take account how a team plays heading into the playoff. And the Falcons are clearly the better team.