The reason most people are dismissive about quality or "taste" in art, or so many other topics, is simply because they have very poor taste -- that is, that the

The reason most people are dismissive about quality or "taste" in art, or so many other topics, is simply because they have very poor taste -- that is, that they are not qualified to judge, or that their judgement is easily influenced by irrelevant factors (like popularity). The reason that the art establishment is dismissive about quality or "taste" is a bit more nefarious, and at least as banal -- they are not good at producing art. So they denigrate that which they know is better than they can achieve. And by their influence (and based upon their degree of control over the opinion-shaping levers) the majority end up rejecting quality -- or being persuaded to reject their own sense of taste.