In fact, the problem has been that rates aren't low enough, they are united by the zero lower bound. The natural interest rate would be several points in the negative.
If you believe that to be true, what rational entity would take the risk of loaning out money to either lose money or get back solely their principal at some future time?
And considering prices are inflating, this makes zero and negative interest rates even worse. Market interest rates reward the savers by risking their capital and loaning it to borrowers who can put that capital to work and pay back the lender both principal and interest.