Cornell University Professor George Warren persuaded FDR, against the advice of all of his experts, to rectify the pent-up deflationary pressures caused by the gold-exchange standard.
So you could even put the switch down to the slow death of that natural deflation built into the Gold Standard (or rather its step-nephew, the Gold Exchange system), starting at the very same time as US stockholders kissed goodbye to earning a premium each year above Treasury yields.
Yet it is the reason government spending has blown past budgetary constraints, revenue downturns, and public outrage since the last check on Federal Reserve dollar-printing ended in 1971 with the demise of the Bretton Woods gold exchange standard.