That's like collector cars that peak in value for the generation after they were made. If it was a poster on your wall growing up, you want it when you are old and wealthy. The generation after is less interested.
With cars specifically it doesn't help that they tend to be a lot less safe to drive the older they are (as health standards have increased a lot over the years), also they just become harder and harder to keep in good shape as the parts become rarer and rarer. Also they had terrible emissions and low gas mileage, so they suck for the environment.
Like I still think some 60s muscle cars look pretty cool, despite being born a couple decades later, but there's no way in hell I'd ever want to own one, for the above reasons. Instead I'll just drive them in video games.
Meanwhile I think it's cool to own a painting brought home from World War II, or a metal cup souvenir from the 1904 World's Fair in St. Louis.
