I have no doubt that in part this is true. Several knowledgeable observers also think that adding Thursday, Monday, Sunday night games to what used to be a Sunday sport have also over-saturated the market. In short, there are probably many reasons, and it is unlikely that Kaepernick is one of the main reasons. But he doesn't have to be the major contributor to the decline in rating s for the NFL to notice that he costs them more than he adds to their product. But it is hard to deny that a large subset of fans were upset about Kaepernick. And I think I should add that in my eyes it is unfair to put this all on Kaepernick himself when the networks went out of their way to talk about it at length every single game. So in an environment where fans are tuning out for several different reasons, no way the NFL is going to deal with some B level quarterback who is a consistent irritant to a non-negligible subset of their fanbase.