Yeah, the old gangster drum-fed Thompson with the ejector thingy on the top (note the professional edicate) looked cool! And they did use it! I think it's the Tompson 1928, what I wonder is why didn't they keep that design, 100 round drum and 600 RPM, it's a nice gun.
I think a more interesting question is 'Why didn't the Japanese develop an SMG. Considering that a lot of their fighting was close quarters in jungle conditions, it would have been an ideal weapon.