I know why. Since it goes to the left every time you put 40 degrees of flap, it means that the flap on the right wing is slightly slower to respond then the flap on the left wing. Although the pilot could react exactly the way he reacts to a crosswind, its a major problem. Just like the left main gear on the A-380. It is 6 or 7 secs slower to react than the right most one... MAJOR disadvantage. If on an emergency landing you forget to put the gear until the last second, well lets say the people on the left die first...