In the NFL, success can be fleeting.
One successful season does not always translate into continued success. Many supposed dynasties have fallen apart after a year or two. Many players have crashed and burned after a one-year wonder. Many teams have suffered injuries or had their luck swing against them. At the end of the day, remaining competitive in this football league is difficult.
One of the easiest bars to measure is a playoff berth. If you make the playoffs, you either have an above-average team or a below-average division. The former is more common than the latter, but both can be fickle things to project for the following year.