What is meant by the statement "Economy beat sentiment and benevolence?"

The conditions of the prisoners on the ship in route from England to Australia were horrible, the death rate increased to a staggering $99\%,$ to change this sea captains were given an incentive to bring prisoners alive. This caused for turnaround, as the results were positive as prisoners landed alive.

Why do you believe financial incentives were such a powerful force to correct a seemingly impossible problem to solve?