It's not "way down." It's about 8% and let's make sure we define "demand" and "interest" and I'm approaching this from an analytics standpoint.
https://www.sbnation.com/2017/7/27/...national-anthem-protests-jd-power-survey-2017
Yes, many things contributed to last year's ratings and I also agree with your premise on Goodell. But interest in the NFL is still off the charts. Last year's Cowboys/Commanders Thanksgiving game was the highest rated game on the Fox network ever.
If you want to say viewership is down it is, and all clues point to a combination of things, most prominently fantasy football and the Red Zone They have effectively killed the three-hour broadcast. Add to that an archaic Neilson rating system and the lack of accounting for other ways to view and you get a false narrative.
In 2017 Fantasy Football will be a 7 Billion dollar industry with 60 million people playing it - up 27% from 2015. Those numbers don't lie.
Last year Twitter had 243,000 people watching a Thursday Night game at any one time and while it may not make a dent in network viewings it is definitely part of that 8% number.
Demand is not down in football nor is interest. Network television viewing has slipped because viewing habits have changed and elements within the game distract viewers and will probably continue to do so. I watched last weeks game on my laptop streamed from my cable company -
Not one single entity accounted for that because there are no metrics to do so.