Damien Hirst isn't an artist. His works may draw huge crowds [...] but they have no artistic content and are worthless as works of art. They are, therefore, worthless financially.
If you want a pickled shark in a tank, you don't have to pay the $12m Steve Cohen paid for the one selected by Hirst. You only pay that much for the artistic content that Hirst has added to it. If there isn't any, what are you buying? You could argue that you are buying an investment. But that depends on people in the future valuing the artistic content in your shark even more highly than you do. If they don't, what are you left with? A shark in a tank, which is what you bought.