They are not always frivolous. For example, I have a car which rolls down the windows about an inch when the door is opened, because the door does not have a frame that fully encases the window. So it's a glass preservation feature in that case, and the loss of the steel to fully encase the window probably saved weight over the window motors.

And TBH, electric motors aren't that heavy. You still need all the gearing and such with a hand crank.