I am doing my rear brakes, pads, rotors, and hardware. My inner rotor and pad was wore right out. I guess my calipers seized. I had installed new rubbers, bolts and pins when I put on my caliper guards last year so this wouldn't happen. Do I need new calipers too? New to this rear disc brake job.

 

Before you install the rubber sleeve into the mounting bracket take a wire brush, emery cloth or a rat tail file and make sure there is no rust or scale in the mounting hole. This will crush down on the rubber sleeve and keep the steel slide pin form sliding. I had one and I tried different lubes and nothing then realized what the problem was and cleaned it out and no problem since.

 

The inners will always wear faster than the outers, just the way the system is designed. How did the sliders and sleeves look? I make it a habit to replace the rubbers every time I do the pads, lube them with a brake lube and like Kowalski said, make sure the holes are clear of scale & dirt. Make sure the pins are clean and lubed.
Make a habit of checking the rubbers from time to time. They get hit with rocks, causing a hole, causing water to get in, causing rust, causing seizure, causing premature wear of the inner pad.
There are some caliper guards you can buy for them as well which really helps this problem.
On the other hand, it MAY be the caliper being seized, but you'd know that when you went to install the new pads.