Gen X-er here…
I, too, remember car shows excluding cars after 1968 in the 80s… Also, growing up in the Midwest, foreign cars, like my 74 bug, were the target of derision and worse. All 4 tires got slashed one time.
Nowadays, I have 2 classic vehicles, the boy has a classic chevy (non-muscle car) and take one or two of them to the car show down the street in the fall usually. However, I feel like the pendulum has swung too far the other way with car shows… Too many 21st century cars are being allowed in and come home with the trophies.
Sure, supply and demand laws do apply. The generations with supposed (disposable) income usually dictate the demand, usually cars from the vintage of their early driving years. Believe it or not, that now means cars from the 80s and 90s,
I never really cared for the muscle cars, not because of their engineering, or because of their looks, but moreso of the crowd that drove them when I was younger. Nowadays, though, I would put to you that people who drive classic cars, (at least 20th century ones) are a more refined, inclusive, and sensible group, even the muscle car owners and drivers.
As far as the market getting flooded with pre 70s cars, heck, I wouldn’t say no to a decent Chevy Bel Air, or an older Ford with big fenders, or even something American with tailfins for cheap, if it could be had, but usually, around these parts, you don’t see that side of it.