I have a road bike and a mountain bike which both use shimano B01S brake pads. The road bike has done 4000km and the mountain bike has done 320km. The brake pads on the road bike look brand new while the mountain bike pads are almost worn out.
The most obvious reason for this is I take the mountain bike on steeper paths and use the brakes more but I use the road bike in the hills a lot and for commuting so I use the brakes on the road bike a fair bit as well. It seems remarkable that the road bike with the exact same brakes and brake pads has lasted more than an order of magnitude more while still being in a much better condition.
I asked some people about this and they suggested that the mountain bike pads would be getting more dirt in them which could be wearing them out faster. Is this a realistic cause for brake pad wear? Should I be cleaning the pads after use?