Is it? I think it isn't at all.
Here's an exemple:
As a Québécois, years ago, when I was younger, many, many Québécois Nationalist fans sat down, or tried to do anything disrespectful they could during the Canadian anthem at sports event. Because they HATE Canada. (Even today, Some Québécois would still rather die then sing the Canadian anthem, I bet)
Now imagine that in 1994, Québécois Hockey players started doing the same thing (kneeling, leaving the ice, whatever...) during the Canadian anthem at games to show their hatred for Canada.... well I am certain the NHL would have stepped in to stop it.
Because, like I said, they want to step away from controversy. And want to be non-political.
It's not a question of identity. It's a question of the league wanting to be non-political.
Altrough, of course, full disclosure, as a Québécois I might be completely misjuging American society. And it's very possible that the peculiar American obscession with the strange outdated concept of "race" (something that isn't even real, we're all members of the Human race, more or less melanin in your skin means nothing).... is so strong that it overpowers regular concerns about business/patriotism/being non-political in the NFL.
But I doubt so.