In an easily-digestible piece for The New York Review of Books, Paul Krugman explains why economic austerity became so mainstream so fast:

Everyone loves a morality play. “For the wages of sin is death” is a much more satisfying message than “Shit happens.” We all want events to have meaning.

When applied to macroeconomics, this urge to find moral meaning creates in all of us a predisposition toward believing stories that attribute the pain of a slump to the excesses of the boom that precedes it—and, perhaps, also makes it natural to see the pain as necessary, part of an inevitable cleansing process. When Andrew Mellon told Herbert Hoover to let the Depression run its course, so as to “purge the rottenness” from the system, he was offering advice that, however bad it was as economics, resonated psychologically with many people (and still does).

By contrast, Keynesian economics rests fundamentally on the proposition that macroeconomics isn’t a morality play—that depressions are essentially a technical malfunction. As the Great Depression deepened, Keynes famously declared that “we have magneto trouble”—i.e., the economy’s troubles were like those of a car with a small but critical problem in its electrical system, and the job of the economist is to figure out how to repair that technical problem.