I think it is because of the volatility of the market. It is very seldom to find stock that changes quickly within a day or even a minute. If you can harness that opportunity you can surely benefit from it by earning lots of money.
Real money isn't like that. Our fiat doesn't change fast, well that is good for the economy anyway. We do not want a money that quickly changes, we atleast need to have a currency that is very stable to buy goods and different things.