Sliders are seized, or move very hard.
The o rings inside the bores that the mount bolts go into have rust behind them, making them grab too hard to the bolt / slider pin , keeping them from sliding easily, this keeps the inside pad applying harder than the outside, wearing them un evenly
Take the calipers off and see if the slider barrels move easily. If not, then pull out the o rings and clean out the rust, lube the O rings with a suit- able brake grease,re install. Dont forget to lubricate the contact points of the brake pad itself, you know...where the pads touch on the caliper mounts. They can become seized at that point also, resulting in the same condition.
Be sure they move freely on the mounts before putting the caliper back on.
Fact is stranger than Fiction