When hardened valve seats production??

In the early 70's The Industry had to deal with two issues, lead and emissions. 60's Mopars could deal with lead free. However, adding the restrictions on emissions at the same time, with the smog controls that followed, Increased cylinder head temperatures, and lean fuel mixtures; This caused premature valve and seat wear. This is why seats were hardened starting in 1972, not the use of unleaded fuel. Older guys can tell you the common complaint with cars from 1973 thru 1985 was:" I smell rotten eggs". Or, why is my engine running at 220 degrees all the time"?
Another common complaint: why is my head cracked? Or, why is there anti-freeze all over the ground after a long day?