Simply because it's easier to keep a wing down than it is to get it back down if it's lifted. That's why.
In that case, we should keep the flaps down, 'cause it's easier to land with them down if we have a hydraulic (or electric) drive failure. Similarly the gear pins should be left in so we don't have to worry about getting the gear down.
ps. In 20 years I've never had any trouble getting a wing down.