Below is speculation....
I wonder if "square" wringer washers were womens' "second" wringer---they wore out one, then were in a market where automatics weren't quite feasible, so got a second, more deluxe in a square cabinet.
Also, given the higher volume of production in the US not sure that a round-forming production line (i.e. round wringer washers without outer cabinets) wasn't way more efficient than producing round tubbed units then putting a stamped steel cabinet around the "works"
Not sure the US ever had a "second" wringer market---I suspect with the earliest automatics (Bendix, Westinghouse) being pre-war, automatics came roaring into the market in the 1947-1949 period just when everyone's old wringer was about worn out. Plus, with Easy in the market for a spinner if milady was a die-hard non-automatic user there were two "deluxe" choices---a square cast-aluminum Maytag or an Easy.