>>4190302because its ergonomically inferior for non-retards who are able to remember that front wheel means aperture and back wheel means shutter. that control scheme was never an ergonomic decision, it's actually based in the cheapest and easiest mechanical routes to each part in a mehcanical body.
the metering is typically in the viewfinder, so the ISO dial needs to be on top so the potentiometer or whatever it's controlling is close to the metering circuit.
the focal plane shutter is accessed by a straight rod down from the top of the camera, also close to the viewfinder, because its clockwork is in the middle of the body and that's where you won't accidentally move the dial, and putting it on front would be even less ergonomic really. olympus put it on the front in a more ergonomic way but it made their lens mount extremely deep.
the aperture is controlled on the lens because it really is in the lens, surprise. an arm in the manual camera just moves it til it hits its stop (which you set with the ring on the lens).
combined ISO and shutter dials follow the same logic - the shutter dial is close to the viewfinder which contains the metering circuit, and on a manual film camera, you do not change ISO shot to shot, ever. that leaves room on the other side for a dial controlling a different circuit like metering/priority modes or a nicer film rewind lever.
the standard DSLR control scheme allows the right hand to control AF, all exposure settings and press the shutter, while the left hand supports the lens or manually focuses. it was almost universally preferred by professionals as soon as it came out.
