I don't work on "big rigs" but I do work on transit busses. The reason that drums are more popular are that they are cheap, and have much larger friction area. The larger friction area means they don't wear out as fast. Big rigs and the like have air brakes, so the line pressure is a fraction of what is available on juice brakes. The drums are huge 16.5" dia and we have them up to 10.5" wide- and the largest ones are ALWAYS on the REAR. My point is that cars and light trucks =/= HD trucks and busses. We had some busses that disk brakes- all 4 corners- and they worked fine, but the pads wore out quickly and the pads would come off the backing @ 5/16" thickness, so we were constantly replacing them.