Originally Posted by
WhyFi
It makes it more likely for debris to stick to the tires, giving them more of a chance to puncture on each rotation, and the wet somehow makes it easier to cut through the rubber, though I'm not sure on the physics of it.
It makes it easier for debris to get a "bite" on the tire. When I rode dirt bikes it was easier to get a flat on wet rocks than dry, at least that was the thinking.