In a ZIRP country, every business that makes a positive return is viable, because there's no outside risk-free option for the capital.

When there are interest rates for savings, only businesses with returns above those rates are viable. That logic trickles through everything. Only workers who yield a return above that rate will be retained. Only products that can be marked up by more than that rate (plus marginal operating expenses) will be sold. On and on it goes.