I'm far from an expert on credit, so I'm posting this, hoping that some of you may contribute to my education.
My understanding is that most families avoided borrowing for consumer goods, except for pianos and encyclopedias, which were considered moral consumption. Then in the 1920s, the automobile industry, facing a stagnating market, encouraged consumers to purchase automobiles on credit.
The Depression and the unavailability of consumer goods during the war left most families in the United States without much of a credit burden. Over time, an increasing share of consumption depended on credit, the absence of which would have limited economic growth.
After the early 1970s, when the great burst of inequality began, the dependence on credit as an engine of economic growth became more extreme.