We've raced a few times at Bradenton, FL's annual Night of Fire where we stayed at the track in our motorhome for a couple nights. We enjoyed our long days of getting tech'd, making time trial passes, then qualifying and eliminations plus watching the other classes. Long and busy weekends. One year we happened to be pitted close to the spectator parking lot entrance and just like s Jim Samuel stated above, the bleachers were empty all day and around 6:30 to 7PM, the fans started pouring into the place. Since we were pitted right behind their bleachers, we ended up sitting with them after we both tanked second round. They saw a great show in about 3 hours and left smiling and happily talking about what they had just seen. It was obvious that the spectators sitting all around us were coming back again.
Compare that to the 8 years when I got free, full weekend, pit tickets to the Gatornationals. I took as many newbies as I could each year and I never got anyone to go twice. (Yes, I had showered.) Even with free great seats on the pit side. To a man, these were car guys. Just not the "hardcore" drag racing-car guys. They were Street Rodders, NASCAR fans, car show guys and mechanics who did know the names of the NHRA stars. None of those I took wanted to be rude so they always hem-hawed their way out of going the following year for another long but free day. (Well, except for my son, but he had no chance as he was hooked as a toddler and my wife didn't want to baby sit or go.)
Seriously, the day IS too long for the "average spectator" and NHRA has to find a new "average spectator" audience every year . It's my guess that if you were able to track all the ticket buyers at a major drag race for a couple of years, you would find that only about 30% return the following year. That number may be to generous. If all the folks that attended a major race came back the next year and only 25% brought a new friend, the tracks would have to add bleachers every couple of years. That is not what's happening. In business, it's always cheaper to keep the customer you already have than to develop new ones. We hardcore will "BE THERE!" Unfortunately, there are not enough hardcore left to support the expenses that have become the norm for the faster classes of drag racing.. The length of the day is why the bleachers are almost empty for final rounds at most all drag races.