Auto racing went into a decline when people's every day transportation became impossible to alter or modify. Cars have become incredibly complex. How many times have you read that there is more computing power in a modern Chevy Impala than there was in the Apollo space capsules. Fuel injection, ECUs, emission control, etc., took the primary source of fun away from the enthusiast - that being engine modification.
And then you have all the safety standards. An enthusiast cannot even put an after market steering wheel in a car now days. Not to mention the overall tightness of packaging which makes working on modern cars far more difficult.
So all that leaves the enthusiast is after market air filters and exhausts - just so long as they're CAT back exhausts - and don't even think about headers because those will flunk the visual inspection during an emissions test.
But fortunately we can still modify suspensions, brakes, wheels and tires; and even do our own oil changes. But even that is threatened. We all saw the all-in-one cartridge that one of the automakers (BMW?) was experimenting with. This cartridge included oil and filter, thus limiting our choice on which brand oil and filter we could use. And it would probably require hookup to the dealer's computer diagnostics system so a code could be reset when it was changed!
[censored], I can't even swap the battery with an identical size and type in my E90 BMW without needing a scan tool. And if I change the battery size and type (like the AGM I recently put in it), I need dealer-level computer diagnostics to tell my car that it has a new battery type!!!
Given all this, it's no surprise that auto racing of all types is suffering. It's not just NASCAR. Four of five years ago I went to the IndyCar race at Fontana. I'd never seen a super speedway race because I'm a road racer at heart. Anyway, the fan base looked like they emptied out every senior living home in the entire LA basin. The stands were virtually empty, 5000 fans I'd guess. And every one of them either had no hair, or had white hair like me!
Here is another perfect example of how things have changed. I read PlanetF1 every morning. They cover F1 primarily, but cover other series as well. Just recently they started covering the video game version of F1. There is actually a series for that kind of racing, one where "world champions" are made. What an EFFING joke!
And with all due respect to the BITOG members here, I don't think there are many true "gear heads" on this forum. The last engine and transmission I R&R'd was the V12 out of my E-type Jag (replaced clutch, engine mounts, and exhaust manifold gaskets). I pulled the engine and transmission in one piece - in my garage. My wife helped me. That Jag was incredibly complex but it was all nuts and bolts, not one inch thick wiring looms that branched off to dozens of unknown electronic controllers and devices.
In summary, it's not "auto racing" that's dying. It's the "gear heads" who are dying, and with that goes the death of auto racing.
Scott