The stated purpose is to ensure public access to creative work, not necessarily to promote the creation of such work in the first place. Copyrights actually do

The stated purpose is to ensure public access to creative work, not necessarily to promote the creation of such work in the first place. Copyrights actually do little to promote broad categories of creative work, much of it being the most important work for society: scientific research. Until the 1970s, copyrights were necessary to ensure that creative work could be disseminated by industrial copying operations, whose profits were dependent on having monopoly positions. These days, industrial equipment is not needed to produce large numbers of copies of creative works, and copyrights have done little to promote more modern and vastly superior methods (such as the one you used to read this comment that I am writing).