The following is excerpted from Clifford Mishler’s Coins: Questions & Answers
Q: Can you tell me why the Philadelphia Mint struck more than one million nickel three-cent pieces in 1881, while the quantities produced in 1880 and 1882 were only around 20,000 each?
A: This is a real mystery that has been puzzling numismatic scholars for well over a century. It has generally been assumed that a heightened demand for the coin was created by a postal rate change, as a reduction in prepaid letter rate from five cents to three cents per half ounce in 1851 had provided the basic argument for introducing a three-cent piece in 1851. That certainly would not have been the case, however, as the next change in the basic letter rate came in 1883 when the rate per half-ounce was reduced from three cents to two cents. The upshot of this high mintage for collectors was the creation of the most commonly encountered and inexpensive type coin in the series in all grades ranging from Good to Uncirculated, although the issue does command a bit of a higher premium in the choice Uncirculated range than any date after 1868.