I'm sure this is meant half jokingly, but American football as a whole is in trouble. Schools are starting to shut down their programs due to lack of interest. Parents, worried about their kids' brain health, are pushing them to play other sports. In time, the talent dropoff will be dramatic enough to significantly affect big college and pro football.
This is a legitimate concern (for the NFL). Fewer children playing will dry up the talent pool in another decade when those children would be at the age for the NCAA and (eventually) NFL. Sure, plenty of children will play, but consider how few of them have the necessary talent to succeed in the NCAA, and how few of those have the talent for the NFL. I did the math once and it is a small fraction of one percent of high school football players actually make it to the NFL, and most of them suck at the sport anyway. At any given time there are only enough good players to make three or four teams in the NFL.
The NFL itself is also really unpopular, with Roger Goodell pissing off the NFL's fans at least once every season and getting booed any time he shows up on TV in front of a live audience (e.g. Super Bowl, NFL draft). I think the only reasons the NFL is still popular are: fantasy football is still a huge thing, even drawing people in that hate the sport (I know people who hate the game but still play fantasy); and some vestigial attachment to one's home team, essentially pride in one's city to include its sports teams.
The decline for the NFL has accelerated much faster than expected. The league's necessary adjustments for safety has made the game less interesting to watch and the recent anthem "controversies" are not helping. Attendance and viewership is down. The decline has already started and doesn't look like it will abate soon. Think that football is too big to fail? 80 years ago Boxing was the #1 sport in America. Look at the state of boxing today.
I keep hearing these arguments, but have not seen any evidence to back them up. Ratings fluctuate, and are on a general down trend, but nothing massive - it is not like the sport is unpopular, it is just not quite as popular as it was previously. It does seem, however, that ratings have followed the general trend of everything receiving lower ratings.
This makes sense, as sports in general (in the USA) seem to have declining ratings. Cord cutting? Younger generation caring less? Who knows? It is a complex issue and there is likely not one cause, e.g. "the NFL is killing itself with how it changes the game."