I have another theory:
1) Right now 23% of school age children are from immigrant families. Families from Africa and India and south America are not US football fans, nor are they likely to become so.
So as the slow replacement of a white population that liked US football, with a non white population that likes the rest of the world football (soccer as it is known in the US) you will see a gradual decline in the NFL. The trend is likely similar in baseball. This seems to account for 11~12% of the decline seen, as I seem to recall reading the decline was already 11 % prior to the flag issue.
2) The ghettoization of football, leftist causes being pushed and the disrespect to the flag are likely a second order effect, which accounts for 5~6 % of the 17 % decline this season.
I was in that category, the last super bowl with its gay pushing halftime show and black lives matter propaganda kind of turned me off to the NFL, not that I was a great watcher prior, but the obvious in our face propaganda did not go over well. needless to say my son will not grow up watching games as occurred in my father’s household.
Kids this days are more likely to be seen wearing a Lionel Messi FC Barcelona jersey than an NFL Jersey.
Also when you have beta male dads and moms ( along with Barky) saying they don’t want their boys playing football. That attitude really hurts long term.