I see what you mean and obviously I agree that something changed. I still think a better explanation is that the country became more conservative when it came

I see what you mean and obviously I agree that something changed. I still think a better explanation is that the country became more conservative when it came to economic policy because it wasn't just the attitudes around the estate tax that changed but rather the entire approach to economic policy. Things like wage and price controls, high income tax rates, and protectionist policies were a thing in the 70s, but became unpalatable in the 80s and 90s.