Pretty stupid question and a really simple answer? Cold feet. And what do you care. Are you part of TSA or some foot police organization. I used to wear wool sock with sandals. Remember the tire tread sandals? It was in Austria in the dead of winter, about 20 below. They ski pretty nicely as well. Here in northern CA in the early spring and late fall why not?. Of course you tuff guys (and gals) with hair on top of your feet probably don't have this problem.
So if you are so tuff, why are you wearing shoes or sandals at all? I suppose you want everybody to be just like you.