Most common reason I change pads isn’t usually because they’ve worn out but to get the drive axle park brake through test.
On trailer axles used to change discs all the time never because the disc had worn out but because the ABS exciter teeth had corroded too much.
Worst case I came across of pad wear on a unit it turned out there was a problem with the trailer brakes - the problem was the driver never put the yellow line in.