Why didn't economists predict the Great Depression?

Economists failed to forecast the Great Depression, perhaps because they had lacked reason to theorize enough about business cycles. Since theory is a public good, the market produces too little of it. The prospect of ex post fame may induce theory; but fame comes from explaining famous events, not from averting adverse events. Also, learning-by-doing induces theory by cutting its cost, favoring the first theories to be developed. These dealt with markets – not business cycles – in the decades before the Depression.