The reasons for the rating decline are many.  Are some viewers tuning out because of anthem protests?  Sure.  But it's also true that the entire pattern of watching TV has changed; the number of people willing to sit through a 3.5 hour game, half of which is commercials,  is growing smaller by the month.  There are other sources available to view game highlights, and in our warp speed world, that's enough for many.  And let's not forget the too-frequent headlines about domestic abuse involving players.  ALL commercial TV viewership is declining and has been for at least a decade; faster alternative entertainment is right there on every phone, and social media is a brutal competitor.  NFL dominance is over, protests or not.