First we had the State Quarters program, which began in 1999. There are now 56 new “America the Beautiful” quarter designs in circulation in addition to the state quarters for a grand total of 112 designs for the same coin. There are also new images of D.C., Puerto Rico, American Samoa, Guam, the U.S. Virgin Islands, and Northern Mariana Islands.
In 2004 the nickel was redesigned with two different designs for the reverse side. In 2005, two more new reverse designs were used.
In 2009 the centennial anniversary of Lincoln’s penny brought us yet more new designs. Add to that the endless dollar coins the public regularly rejects.
NONE of this redesigning is for security reasons. It's all cosmetic and trivial. It's expensive to commission artists and cast dies. Enough with the redesigns!