Why uneven wear left rear brake pads only? on 2009 Toyota Matrix

1 side all worn the other 90% okay. At the same time no problem with the right rear pads other than a slight angled wear on both sides. Changed pads and within 2 years needed replacement again. Rear pads need replacing twice for every one time in front. currently at 60k km.

Asked by for the 2009 Toyota Matrix
sounds you either have a seized caliper or the slide pins