Why is it that people with handicap parking placards (or stickers, or plates, depending on your area), which should indicate the presence of nothing more significant than a physical disability that limits one's ability to walk (not that such is insignificant, but that it is entirely unrelated to the difficulty that will eventually be pointed out in this sentence, should I manage to quit digressing) drive like they're mentally handicapped, instead?

Inquiring minds want to know.