...at this point in time , carbines , garands ,Bars, M1911s , M1919A4s , etc. were still primary , standard classed weapons. M1928 thompsons were limited standard with the M3 and M3A1 greaseguns as the then current standard. It was just unwise , with the war and all , to justify the time and expense to install the parking equipment in plants for a weapon system that would be shortly discontinued when M3 production met demand ( and the M3 was parked).
Chris