There was no "Retro" back in the 60's because from the 30's until the early 70's the cars that came out on the market were better than the ones of previous years. There was no need or even a market for retro. In the mid 70's when the Gas Crisis hit the market changed to small cheap gas thrifty cars with very little to attract the true car Guys.
This seems to be the trend up to today. Thou the cars are more advanced and are safer, faster and more driver friendly they don't appeal to the earlier generation Car Guy. The "Muscle car era ended in the 70's and there is still a market for them. There were a lot guys that could not afford them back in the day and now they have the funds but the original cars are still way up there in price (no thanks to Barret Jackson) but you can buy a retro Challenger, Mustang, Charger and a couple others for a reasonable amount.
That is just a point of view from an "Old Car Guy"