Some are due to lack of any fashion sense or a good stylist. But sometimes those items that seem not to match are used to accentuate the ensemble. Being too matchy is not a good thing. For example if you wear all black none of the pieces will stand out, but if you wear different colors each one will stand out on its own. And those who do that actually do match, its just sometimes they are odd combinations that most of us are not used to, but they still fallow through using complimentary colors. In the color wheel there are colors that are opposite and colors that are complimentary. Someone who doesn't match actually has to be wearing opposite colors from the color wheel.