First, they made insuring a muscle car unaffordable.
I'm sure it wasn't all of those 'coming of age' baby boomers wrapping their GTOs around trees that had any effect on insurance rates.
Lost two good friends around 1969 or so to losing control of their cars on the country roads in northern Michigan. Both alcohol related.
The most tragic one was Randy, the owner of his 57 Chevy was too drunk to drive so his buddy Bob decided to drive them home and he lost control of the car on the back road, and Randy was killed while Bob survived......