Not sure, but robbers most likely focused on Oklahoma due to the poor state of the economy due to failing agriculture. Farmers were unhappy with the high taxes they had to pay, and often looked at bank robbers as heroes. This stood as citizens enabling bank robbers.
Explanation:
Oklahoma was in a very bad economic state after the World War as most of the economy was based on the work of tenant farmers. After the war, less agricultural resources were needing, leading to a failing economy. Many farmers and citizens blamed the failing banks as well as they still required high taxes for farmers. Here's a helpful document I found: https://www.gearyschools.org/vimages/shared/vnews/stories/522f9e3953516/Chapter%2013%20%20How%20did%20people%20in%20Oklahoma%20deal%20with%20the%20Great%20Depression.pdf
Oklahomans reacted mainly with resignation as the depression wore on. There was a food riot in 1931 in Oklahoma City and other peaceful protests in that city and in McAlester. The Farmers' Union revived, and the Southern Tenant Farmers' Union recruited, somewhat ineffectually. Hope that helps
