>>3378226>I imagine it's because back then it was easier for the body to choose an aperture than adjust the shutter speed.Aperture priority was actually easier to implement. shutters went electronic in the mid 70s, with the speed contolled by ICs. To get A mode all the camera's computer needed to know was the exposure meter data and the lens' set aperture via the offset of a brush resistor, mounted somewhere around the lens bayonet, that moves when you move the aperture ring. No need for any mechanical coupling to move the speed knob. In fact, most A cameras use "stepless" shutter speeds set by the computer, not otherwise available on the manual mode.
whereas with shutter priority you need extra hardware in the camera and the lens to mechanically move the aperture lever to step down the lens' aperture to the value set by the computer, and not past that point.
that's why most camera brands had to introduce updated lens mounts to be able to get S and P modes: Canon FD, Minolta MD, Pentax KA, etc. while the then new A mode was usable with existing lenses (minolta MC lenses from the mid 60s work fine on the A mode from '80s minoltas).
