Ron,
Well, they probably just got 'em cheap
I'm thinking in lines of river police or coast guard issue as the Navy remains effective as an intermediate distance weapon.
In those days, Dutch police viewed the 9mm as too large/powerfull. Regular issue guns used the 7.65 browning or 7.63 or 6.35 calibers.
What is funny is the remark of the author that so many policemen were walking around with too little knowledge of handguns in the 1930s. The same discussion is held today in 2004. Some things never change