They weren't. To think that they were is to misunderstand the cause and effect of the credit crunch and ensuing snafu.
They found new ways to exploit the markets within the law and sometimes outside the law and didn't have enough actual money (thanks to ignoring the law) to pay for their gambles when they went tits up. Gambling.
They found new ways to exploit the markets within the law and sometimes outside the law and didn't have enough actual money (thanks to ignoring the law) to pay for their gambles when they went tits up. Gambling.