Certainly, there is saturation which we all know. NFL has Sunday, Monday, Thursday and late in the season Saturday.
But my thoughts are contrarian. You would think parity makes everything more interesting. I think it's the opposite. I think the NFL needs at least a couple of dominant teams. When you had whichever teams being the dominant teams, there was interest in seeing if there could be upsets. Now every game is hard enough to pick winners versus points. I see this in other sports as well. Tiger in golf, Tyson in boxing, going back Borg/McEnroe in tennis.
In the NFL, there is nearly a 50-50 chance of your team winning or losing when you factor in home versus away. I think people are less interested in watching when their teams have just as much chance of winning or losing.
Seems completely opposite, but my thoughts are that the parity where everyone is between 7-9 and 9-7 hurts interest across the board.