The driver's position is closer to one mirror, so he or she can simply move his head up or down to get a better "vertical" field of view. So the driver mirror is longer to compensate for the angle, as well as closeness of the driver.

Passenger side mirror is farther away, so any driver movement is not much of a difference. So it is taller to give the driver the "same" kind of vertical field of view.

With the closeness of the driver to one mirror, only a lever is needed. Vice versa with the other mirror.

They did the same with the W124, but the later models had a switch you could use to adjust both side mirrors.

The W123 mirrors look the same from the front but are actually angled differently.

Same question for the wipers - why change them over the years, right?