I don't doubt that those players feel what they are doing are right. But there are plenty of folks that are punching out of watching and attending because they aren't interested in the political views of the players. The NFL watching demographic isn't primarily hard left social justice types. Trying to blame the fallout on anything but the actions of the players (Russia, racists, Trump) is really just whistling past the graveyard.
I personally give zero shits. I haven't watched an NFL game in years. I was a fan back in the day where the team mattered. Unrestricted free agency was the point of exit for me. I don't watch any pro sports these days, except mixed martial arts. The latest Jon Jones bullshit and the over the top greed displayed in the Mayweather McGregor fight now has me questioning why I waste time watching it.