I've got the secret. Are you ready for it?
It's not weird start times of games from London. It's not Colin Kaepernick, no matter what your cranky uncle might say. It's not any of the million and one convoluted reasons people are coming up with to avoid the simple truth.
And the simple truth is, thus far, the games have stunk. The marquee franchises have, by and large, been either awful (Carolina) or boring (Denver). Star power is down, with Peyton Manning gone, Tom Brady MIA for four games, JJ Watt going out for the year, Cam Newton getting the full Aikman treatment, and Aaron Rogers suddenly slinging the ball like Fred Rogers. Games that in the preseason looked like compelling matchups - Giants-Packers, please! - stand revealed as slugfests between mediocrities. No one has enough depth, salary cap issues force massive roster turnover, leading to the rostering of unprepared and inadequate cheap talent in order to scape together a few more bucks under the cap.
The inestimable Mike Tanier goes into more depth on this here, but the basic takeaway is simple: Worse football means people turning off sooner. People turning off sooner means fewer people watching at any given moment. Fewer people watching means lower ratings. QED.
And if you don't think this has something to do with the league's attempt to grab every last possible dollar, squeeze into every possible programming niche and grab every moment of the spotlight possible, the talent and the on-field product be damned, then you haven't been paying attention.