I am an old guy so I have seen these power wars before.
Up and into 1970 cars were making power, not like our 700+ hp cars but they were fast, and sometimes dangerous.
1971 about have the care came with lower compression, etc.
1972 it was all over.
I was young at the time so I don't really know the whole story.
I do know insurance companies jacked up the insurance really high on performance vehicles and some vehicles they would not insure at all.
People quit buying them.
Compression kept dropping, smaller valves in the heads, no more forged motors etc.
From what I remember (and that's not much) it was all the insurance companies doing, but I could be wrong.
Hope it does not happen again but if it did the value of our cars would shoot to the moon.
My.02,
Varooom