I think this is a little bit of a misnomer.
Other than Notre Lame, the top 3 teams in the "Playoffs" are 1-2-3 in scoring D.
https://www.ncaa.com/stats/football/fbs/current/team/28
And yes the Saints are an outlier, but the division leaders in the NFL are all in the top half of the league in Points Allowed.
http://www.espn.com/nfl/statistics/team/_/stat/total/sort/totalPointsPerGame/position/defense
I'm guessing YoY the numbers are looking worse, but comparatively speaking in a season you need to at least be "league average".