My guess would be that it has to do with the speed of the ball at impact with the target. The faster the ball is moving, the greater the chance of it ricochetin

My guess would be that it has to do with the speed of the ball at impact with the target. The faster the ball is moving, the greater the chance of it ricocheting off the rim as opposed to being slowed by the impact with the rim and falling in. Maybe the ball would have only a 50/50 chance of falling in rather than out, but that's still better than if the ball hits the same spot at high speed and ricochets. In other words, by slowing the impact speed with the target you make the target more forgiving. Btw I'm not an expert in ballistics, so this explanation is probably complete bs but it's interesting to think about.