To force a total power disconnect is my guess. Unplugging things is actually kinda "old school common" too. With all the great design of the past, there was some real fire trap crap too.. the UL did a world of good there.
I've meet plenty of older folks that unplug everything not in use. Especially toasters. I don't think many families broke the habit until TV's and radios began to no longer need a warm up, or maybe the earlier Sunbeam coffee pot getting left on warm half the day.
If you could afford the power leak you likely didn't care. A transformer is pretty stable and power there low voltage.
Many early houses around here didnt have overhead lighting but a switched outlet and lamp or wall sconce was more common in most rooms than today. (Most living rooms retain the feature). The use of screw in converters for light bulb or fuse base to a blade type outlet was also common. I've been in homes with no plugs just wall lamp outlets, and nothing but unswitched lamp plugs at 5'. Uninsulated bare wire run to ceramic posts and spaced a foot or two apart or in separate wall /ceiling sections.... Old electrical is crazy at times.