I think that the mistake you make is assuming that "the big boys" think the same way that you do.
They don't.
Banks are in the business of making money to keep their shareholders happy. Bank shareholders don't like surprises! They like nice steady income that grows over time.
Gold has no income, and is wildly volatile. Bankers don't like that, so they don't invest in gold.
However, they are happy to buy and sell gold in physical and derivative form and take a nice margin on each trade that over time delivers the steady income that their shareholders want to see. In the context of the gold market, they are "a nation of shopkeepers".
