The funny thing is Thompson submachine guns weren't ever big sellers because they were prohibitively expensive. They were hand machined, Union-made, and incredibly complex for the era. Throughout WWII the military was trying to replace it with a lighter, cheaper, less labor intensive gun (failing with The jam-happy Reising , succeeding with the M3 grease gun). The Chicago outfit was the only significant criminal organization that used them up until the NFA passed. Hollywood contributed a lot to it becoming so iconic as a "gangster" weapon, and a lot of those used by actual gangsters weren't legally obtained.
Of course Bob still thinks it was rivers of blood in the streets then, but these events were and ARE anomalies. It's largely a pop culture and pop history based impression. Not that I expect Bob to have any connection to reality at this point.