I think almost every guy's had a thing for skirts ever since he saw a good looking girl with one.

Sure, it's wrong, but when you see a hot girl, you just want to know what's under there. Or lack of what's under there. Perhaps think of what kind of panties and/or the color or if she just happens to be hiding a small vibrator in there. I suppose there's always a chance, after all.

Then there's the sex part. It's pretty much easy access. And because of that, it's easier to do some public sex activities. I personally just like the idea of a skirt covering the lowers during sex myself.