That’s a valid point. I would look at it like NASCAR’s situation over the last ten years. They peaked in popularity and then their ratings (and ticket sales) dropped very quickly. In the entertainment business, what you find is that once you get outside your core fan base, people tend to have very short attention spans.
Don’t think that that’s the case with the nfl. College football is still hitting new highs this year. Almost guaranteed it’s the kapernick effect.