Hard to choose between the lesser of two evil empires sometimes? ;)
Unless George had a "no sequels" clause written out somewhere, somebody was bound to float sequels sooner or later. Some fantasy universes are just too tempting not to revisit. (Disney has a Wizard of Oz prequel in the pipeline, and there have been many books not penned by L. Frank Baum.)
George's kids might have wanted to make new films someday, but we'll probably never know now.