The Tale of Despereaux: Being the Story of a Mouse, a Princess, Some Soup and a Spool of Thread has quite a descriptive and lengthy title. It tells readers that the main hero of the story is someone (or some critter) named Despereaux, and that there are lots of other parts that make up the story—like a mouse, a princess, some soup, and a spool of thread.
That long title is also reminiscent of a lot of 19th-century novels. Like The Personal History, Adventures, Experience and Observation of David Copperfield the Younger of Blunderstone Rookery (Which He Never Meant to Publish on Any Account), aka David Copperfield by Charles Dickens. It's consistent with the writing style in the rest of Despereaux.
But even with all of this, the words don't reveal exactly what the story is about and instead act as intriguing little hints to draw the reader in. After all, wouldn't you want to find out how all those different things go together?