1960s America led to 1970s America, which had a lot more concern for the environment. It's inevitable that as problems accumulate, people affected by them will want to do something about it.
1970's America wasn't anywhere near as poverty struck as China. It's really difficult to care about the world around you when you can't even take care at home.
In 1975 the US GDP was about $7500/yr per capita (in 2021 dollars). Today the Chinese GDP per capita is around $10k/yr (more like 19k accounting for purchasing power parity).
The 1975 US Household median income was ~$13,000 (approx $65,000-70,0000 in 2019 dollars) [0][1]
Chinese household median income is around $4,700-4,800 in 2021, with massive disparities between First world comparable regions such as Beijing, Shanghai, and Tianjin, and rust belt regions like Wuhan [2]. Even the Chinese Premier Li Keqiang has noted that 600 million Chinese earn less that $140/month [3].
This of course leads to the larger discussion about GDP per capita being a weak metric to use when analyzing regional development, but in general China is by most standards still a developing middle income country with a (relatively) small and overperforming hinterland.