I'm not sure why people think the 1970s were so conservative. Nixon wasn't a conservative, Ford wasn't a conservative, and Carter wasn't a conservative. And with the exception of the 1978 election, there wasn't much GOP success to be had anywhere. Pop culture seemed pretty liberal too, from the Studio 54 to Charlie's Angels to Three's Company. Politically, we almost had the ERA, we got expansions in the Clean Air Act and the launch of modern day environmentalism, relations with China, and arms treaties with the USSR.
I think that's when the bloom started coming off the 60's rose. People interpret "less liberal" as conservative.