Leverage is only possible if there are funds available at low interest rates, compared to what money managers think they can get somewhere else, usually involving some high risk speculation scheme. This is so only because there is too much capital available compared to the need for capital. If there were productive uses for the funds at reasonable rates why would holders of the funds being willing to lend them out at low rates to money managers who want to lever up some speculative scheme?
Our financial problems today are largely a result of money managers using leverage to increase yield at great risk, and then buying phony insurance in the form of credit default swaps (CDS) to guarantee their risky investments. Unlike real insurance, CDS don't require any reserves to pay off if the investments go bad. Also, they don't require that the purchaser own the asset being insured. So an outfit like Goldman Sachs can buy a CDS on some collateralized asset they don't own, and then proceed to drive the price of that asset down so that they can collect on the CDS.
Talk about Ponzi schemes, this one doesn't even require convincing investors to give you their money.