As usual, many many excellent points on here.
For me personally the product itself is watered down. Too many flags, replays, antics and other shenanigans are my guesses. When I talk to people "at the water cooler" it seems to be what others are saying too.
MNF used to be a ratings gold mine and must see TV. I remember looking forward all day to coming home and watching that. Can't remember the last time I watched one beyond halftime.
Netflix, HBO and other outlets are producing some of the best shows in recent memory (Game of Thrones, The Wire, House of Cards). There's more talk of that than the NFL anymore.
I still watch, but not at the level I did in the late 80's and 90's.