A policy of very low interest rate levels favours borrowers but penalises lenders, and if the economic crisis is associated mainly with a lending crisis, a policy of extremely low interest rate might be counterproductive.
If the rate cut stops at a higher level, consistent with the medium-term inflationary projections, it is more likely that the interest rate will remain at that (above zero) floor level for some time and lenders will be more inclined to invest in long-term risky assets.