The following Q&A is excerpted from Clifford Mishler’s Coins: Questions & Answers, 5th edition:
Q: Are there any specific reasons why the United States does not change the design of its coins as frequently as do foreign countries?
A: A law enacted by Congress on September 26, 1890, specified that changes in the design of regular-issue U.S. coins cannot be made more frequently than once every 25 years, unless Congress enacts legislation mandating a specific change.
Treasury officials have historically maintained that the counterfeiting of our coins and currency is made more difficult by infrequent design change, reasoning that familiarity intimately acquaints the public with the designs and enables them to more readily detect counterfeits. (If you believe this reasoning to be valid, ask a non-collector to describe the reverse designs of the coins in his pocket change.)
The validity of this historic reasoning has been invalidated by the experience with recent special issues of circulating coins, specifically the Bicentennial-coin issues of 1976, the 50 State Quarters® Program of 1999–2008, and the innovative Westward Journey Nickel Series™ of 2004–2006. The nickel experiment, in particular, may lead to a more enlightened approach in the future, although the likelihood of the retention of Lincoln, Jefferson, Roosevelt, Washington, and Kennedy portraiture on the obverses of the cent, nickel, dime, quarter, and half dollar, respectively, is highly probable given historical and political considerations.