I seems to me that many people enjoy the NFL as a respite from America's culture wars. If the NFL wishes to become just another battleground then be prepared to lose viewership and prestige.
I was amused during last year's Super Bowl to see commercial after commercial touting various social justice causes - all occurring, of course, during a break in a game in which men beat the crap out of other men, for the amusement of other men. It was a startling example of Madison Ave ad execs falling over each other to prove themselves the most progressive, all while entirely misjudging their audience and why people engage with the sport to begin with.
Then came the great re-set at ESPN, in which the corporate powers that be chose to purge many of the long-term sports journalists - people focused on the sports themselves - in favor of social commentators and talking heads. What are they thinking? Unless the corporate powers are just looking to pat themselves on the back.
Now we have the latest Trump s-storm. We should all be aware of the carnival barker and what his tactics are. The point of what he said is not to get NFL teams to actually fire players for kneeling for the anthem; his purpose was to rouse the passion of players and media SJWs to protest further, and thus make them look even further sundered from the viewership who are just trying to enjoy the game as entertainment. And what do the players and owners do? Do they hold their heads high, say we're professionals, we dance to our own tune? No, like the rats of the pied piper they line up to play the part of "outraged spoiled millionaire" assigned to them.
As Koopa said above, the NFL has changed, and there's no natural law saying it will always be the most popular sport or past time. If the league, advertisers and players all wish to conspire to make the game just another vehicle that adds to the bitterness of our times, they will pay the price for it.