The only way for banks - who run such an economy - to make more money is to lend more out. So they looked for more borrowers, as well as more places to park their cash. As a result, the things you and I depend on in the real world became investment vehicles. Homes, oil, resources...you name it. So the costs of all these things went up not because of any real laws of supply and demand, but because they had become new classes of investment.