I don't think this is a new trend. It has been trending this way for a long time. How many years has it been since Tri State quit racing weekly? I believe it was the first. Kokomo gave up on it a few years ago. I think there are several factors.
1The cost of insurance for a night is extremely high. Don't know for sure what the exact cost is now, but was told by a promoter over 10 years ago that the first 100 tickets sold covered his insurance. To cover that, admissions were raised, and you have even less people that can afford it. To cover that you add more classes. This makes for a long program and is tough for families to attend.
2 Racing has become a more participant more than spectator sport. Look how many people who used to go the track, that are involved in micros now. If you look, those are getting ridiculously expensive anymore. Racers can be their own worst enemy when it comes to spending.
3 It is hard for a racer to justify risking his investment, for $1400 to win. I knew a guy who had a thunder car who had $35,000 in his motor. There was a hornet team at Gas City that I heard spent a fortune. How many people did those discourage from racing, because they knew they couldn't compete? So, you have a bunch of classes with very few cars, and only a couple have a chance to win. Not exactly must-see entertainment.
4 Growing up in Kokomo, there were 6 or 8 sprint cars parked outside gas stations when I was a kid. Now those gas stations are convenience stores instead of repair shops. Those cars raced mainly at Kokomo, and now tracks seem to be competing for the same cars. You run a couple of tracks, and the season has gotten much longer, and that makes it more expensive for the racer. When the local guy doesn't race anymore, you lose his neighbors and work buddies who came to watch him.
I am sure I can come up with several more reasons, but it doesn't matter. It has been coming for a long time, and I feel like the time to save it has probably passed a long time ago.
With all that said weekly racing does seem to be doing good at Putnamville, and Paragon seems to be building it back up.