As long as one doesn't understand that America's top social class was hereditary it will be impossible to understand that it disappeared in 1960 and even harder to understand why it disappeared.
Many, if not most, people think the top social class is based on wealth. Not so. The wealthiest corporate Americans are invited to Herb Allen's annual soiree in Sun Valley every year. None of them come from the old hereditary classes, including the hereditary class that built Sun Valley...the Harriman's.
Corporations are terrible places to find jobs for the friends of wealthy corporate Americans (unlike the old days when the elite got top jobs for the children of their peers). It does happen, but it doesn't last long because merit or lack of it are very quickly apparent. Merit is what commerce is about. The old top elite class always provided jobs for the children of other hereditary class members, regardless of merit, just as they still do in England, France and most of the rest of Europe.
The moneyed top people of America get little or no benefit from their high income status. In the old class structure everyone high-up in their field knew everyone else via clubs, schools, marriage and endless society gatherings. Today, the top people don't know any of their top peers.
Members of the top economic cohort in America don't know each other. In Lerner, Nagai, Rothman's book American Elites they reported on their survey of the top 150 people in 12 fields..law, media, corporations, government, military, religion etc. Not only didn't these leaders in their fields come from elite schools, the vast majority of them came from blue collar or middle class families. When shown a list of the other leaders, say the top media people looking at the list of the top financial people, they rarely knew each other...rarely.
They are simply not a part of any class...not a coherent class, not any class.