Tell that to Dillenger, Machine Gun Kelly, Ma Barker, Al Capone, Pretty Boy Floyd, Bonnie and Clyde, etc., etc., etc.
How many of them were active before 1929, and how many only afterward? How many were created by prohibition?
My understanding is all were in the early 30's. The only one really involved in prohibition was Capone and he actually was in business prior to the Depression. Even he stayed in business during the Depression and actually ran soup kitchens in Chicago for out of work people. All the others were basically bank robbers although they would hit stores for quick cash.