The SJW pollution of a non-political product wouldn't have been enough on its own, at least not this quickly, but it does look to have compounded the problem. They're making it easier for the customer to say No when faced with the prospect of spending X amount of money for Y entertainment. You never, ever want to make it easy for the customer to say No. Marketing 101.
A brand in decline needs to be rejuvenated, and it won't be by turning the players into political hipsters. I get the impression that certain influential voices (coughcoughESPNcough) felt that promoting social justice on the field would actually improve the product's attractiveness. The customers disagree. Obviously.
Social justice wasn't emphasized to improve the product offering, but rather it was a device to (hopefully) expand into new market segments.
50% market share wasn't enough for some; no, they wanted to go whole hog. But in so doing, they made the mistake of alienating their existing 50%. Even worse, what the NFL is finding out (the hard way), is not only do the new 50% not really care, but they certainly won't go if the baseline 50% is actively pissed off and boycotting the program.