I presume it's basically the reasons stated. Much less material to catch wind (in pleated skirts). And many skirts aren't pleated at all, just wrapped around (basically) and therefore have little slack to be caught and moved by the wind.

I was at church once with the girlfriend, and she had on a skirt that was pleated all the way down. It was a windy day, and we walked outside. She had to catch the skirt that had come flying up and walk the rest of the way to the car holding the skirt down. So it does happen