If the handbrake mechanism inside the caliper is sticky, maybe it's not releasing. Then one rear brake will drag, wearing out faster than the other rear.

Replacing pads won't fix that. It's not really an adjustment, either. Figure out why it's sticking & fix THAT. Maybe the cable is corroded inside it's housing? Maybe something's fouling up the cable under the console? Maybe the spring/lever on the caliper is rusty/sticking or screwed up somehow?