If a lot of money goes into the stock market, it'll push up prices, making money for stock speculators. Then the insiders can decide that it's time to sell out, and the market will plunge.
Most banks - with Deutsche Bank at the top of the spectrum here - have decided that they can't make money lending to barrowers anymore, so they're going to the second business plan: They lend money to casino capitalists. That is, to people who want to gamble on derivatives.