Even among non-NFL events NASCAR is a good deal behind other sports. The only two NASCAR events ranked in the top 50 of non-NFL sporting events in viewership last year were the Daytona 500 (#8, 16.65 million) and the Subway Fresh Fit 500 at Phoenix (#41, 9.12 million).
Yeah, Nascar is well behind the top team sports in America. Everybody knows that. This isn't a new thing.
If you compare top events then the top NFL, College football, NBA, College basketball, and MLB all draw more viewers than the top Nascar event.
Most people aren't Nascar fans. Motorsports are a niche sports.
Of course, Nascar peaks higher than horse racing, golf, NHL, soccer, tennis, UFC, and boxing. A lot of other niche sports would love to have as much mainstream acceptance as Nascar.
Nothing shameful about being a successful niche sport. Obviously Nascar is always trying to grow and get more mainstream fans. So is every other sport.
NHL launched the Winter Classic and all these outdoor games to attract new fans. Golf added a playoff system just like Nascar, the Fedex Cup. Fedex Cup has been mostly a failure as golf fans mainly just care about the majors.
In many ways, every league except the NFL is a niche sport in modern America. There are so many TV shows and movies and sports on TV. There is so much time spent on videogames and the internet. Audiences are fragmented. That seems unlikely to change in the future. Every sport and league is trying to hold on to their fans and attract new ones.