Wing down gives you crossed controls on the approach anyway. Given how ineffective Cub (and most older light aircraft) ailerons are, using the rudder to stop a wing drop due to gusts is a much more natural reaction. As beagler says, it accelerates the dropped wing and thus picks it up. Maybe it's also something to do with the fact that taildragger drivers realise that the rudder pedals are more than just a convenient place to rest your feet.
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When the wheels stop turning you're high enuff. CubTrek. To slowly go...