Simply put, going to NFL games has become a rich (or at least upper middle class) person's thing to do. The days of packing stadiums with 100K fans are over. Just like baseball stadiums got smaller (Compare Jacobs Field to Municipal Stadium, New Yankee to Old), NFL stadiums have gotten smaller.
With PSL's and/or club seats, virtually all of the lower bowl, mezz seats on the between the 20's are a serious expense.
The makeup of Metlife Stadium fits the "new" profile:
1) Rich people (and corporate hospitality) in the really good seats;
2) Middle and Upper Middle Class in the endzones and corners; and
3) Upper Deck: this area will be where they try to make sure the game stays relevant to the masses. Keeps those jersey sales going.
The big money to NFL teams will come from TV packages, advertising tie ins, and big money guys in the lower bowls.
Full Disclosure: We have seats in the LLEZ. Doing well enough to spend money on things I enjoy, but not the FU money to sit in clubs.