Seeing the right angle of things

From the September 1937 Popular Science Magazine:

I know we can buy such things on selected electronics now... such as

GE Wall Hugger Extension Cord

But the thing is, if this is a good idea, as evidenced in 1937 and again now, what about all those years in between? Why did we stop doing flat plugs that allow us to push furniture closer to the wall without bending the cords into unsafe positions and/or knocking the plug out completely? Why'd we stop doing nice tidy flat plugs in favor or plugs that stick out of the wall nearly three inches?