Can anyone help me? Dr. Kling?

Central-bank intervention has kept market interest rates low for several years, but only by monetizing government and TBTF debt. Private lenders would like to demand higher interest rates but are competed down by central-bank money-printing. Private borrowing seems low despite the low interest rates mainly, I think, because of credit rationing and the difficulty of identifying any investment likely to earn more than even the low nominal interest rate on borrowed capital.

It is a truism that on average over some time all investment classes offer the same return (net of taxes and some allowance for risk– and subject to Eric-Falkenberg-type envy effects), because any class offering outsized returns attracts more investment until competed-down to average. So in theory when the central bank says it will supply funds to any investment at a very low rate, no entrepreneur will pay more than that rate for funds, so no investor can expect to earn a return over that rate; possibly not even equal to it, net of transaction costs unsubsidized by the central bank.