Analysis of some of the early manuscripts of the Canterbury Tales suggests that Chaucer originally intended to assign the Wife of Bath the tale that is now attributed to the Shipman. Some people think that, as the Wife of Bath's character developed and changed from a relatively simple character to the larger-than-life and complex form in which she now appears, Chaucer decided that she should have a more "important" tale.
We're not quite sure what makes "The Wife of Bath's Tale" more important than the Shipman's Tale, but it is certainly an appropriate tale for the Wife of Bath. Unlike some tales, which seem only marginally or not at all related to their tellers, this tale fits the Wife of Bath's character fairly well. It's a Breton lai, or short French romance, which was a genre associated with a female audience in the medieval period. Not only that, but the subject of the Knight's quest in the tale is the answer to the question of what women want, which was one of the subjects of the Wife's Prologue. And the answer to the question – sovereignty – is exactly what we expect after having read the Prologue.
This is a tale in which women not only desire sovereignty, but get it. The Queen and her ladies administer the knight's punishment for rape and back up the loathly lady in her request to marry the knight when he's unwilling. Appearing chastened by his wife's wedding night speech, the knight yields 'maistrye' in the marriage to her. It's an ending that echoes the ending of the Wife's Prologue and a tale which, like that ending, seems like it could be the Wife's fantasy of how the world ought to be.