Because of weight transfer, there already is more total force pushing the outside rear wheel into the road. The inside rear wheel gets lighter, so increased downforce on the inner wheel attempts to compensate. It probably also reduces body roll, preventing the outer wheel's camber from going positive...Aren't they lifting the wrong side of the wing on the turns to produce more down force? Wouldn't you want more down force on your outside wheel as that is the one that would start to slip first?