Of course, the explanation is rather simple: as people cross from informal employment [into formal or salaried employment], like those employed in farming where kids get fed rather than get wages, as you transform the economy into something more modern, cash is actually gradually being introduced to those parts of the economy.
Therefore, we take very seriously our role as the printer of the physical cash, that the bills look good and they are always returned on time so that the unfit bills are replaced as quickly as possible. To preserve currency integrity, we implement the Clean Note and Coin Policy and the Coin Recirculation Program.