The prices of all goods and services in the economy are determined by the intersection of supply and demand. Central banks exert enormous influence over the money supply, and therefore the price of borrowing money is influenced by central banks.
In the absence of central banks it's likely the world would eventually settle on a single commodity to be used as money, and it's unlikely to be a commodity that's inflated into oblivion like fiat currencies. Additionally it's unlikely that people will somehow start loaning out money for a rate of almost 0%, why would people loan money (and therefore risk losing it) for a return of 0%? They'd be better off just holding onto it.
