This is not a question that I have ever asked myself, but my first inclination is that Chaucer does not expect that these people are capable of changes—or in some cases that they should change.
For instance, in Chaucer's "The General Prologue" to The Canterbury Tales, one of the first characters he describes is the knight. This man has proven himself to be valiant and noble. He is a great warrior who has fought in many battles. He is a seasoned soldier who has traveled the globe. The first thing he does when he returns home, this man of humility and faith, is to join a pilgrimage to the Canterbury Cathedral to give thanks for his safe return home. There is no need for this man to change, but the fact that he has been fighting for so long and never boasts of his accomplishments but goes to pay homage to God for his deliverance yet again, gives me to believe that these are lifelong patterns that will not be changed.
The Wife of Bath is looking for her next husband, and she has buried quite a few. The inference is that this lusty woman may have worn her previous husbands out in the bedroom. She is a successful business woman in her own right and has been on a number of pilgrimages to show her faithfulness. She is hoping that this excursion will find her a new husband, but her work, her travel and her pilgrimage are things that have developed over a long period of time. I would think she believes that what has worked so long should not be changed.
Looking to the other end of the spectrum, we see the Pardoner and the Friar who are men who have found a way to bilk the system. They are dishonest and/or disreputable. (The Friar seems to get girls pregnant and then find husbands and homes for them. The Pardoner sells stolen pardons to people—pardons which are supposed to cleanse them of their sins. Not only does he sell stolen goods, but the Church receives none of the profit: he keeps it all for himself.) These servants of the Church who should be seeing to the needs of their parish and the decent souls they meet along the way have a great set-up in place. They show no signs of being ashamed or humbled by anything around them. They will not change.
The Parson is a man of God who gives his time, his energy and his worldly goods to those less fortunate. He wants nothing for himself: his only goal is to ease the suffering of the poor and guide souls to Christ. He has no intention of finding an easier path. He is not critical of others. His concern is to serve his congregation as best as he is able.
It is probably important to note that Chaucer does not draw attention to the shortcomings or accomplishments of any of the members of the pilgrimage except from within his tale. This epic poem describes the kinds of people that Chaucer has met in serving the British Crown. In providing the King service in a variety of capacities, Chaucer has interacted with people from all walks of live, all socioeconomic levels in medieval England. He does not pass judgment, though he definitely points out the failings of many of these people with "tongue in cheek." Chaucer is a student of human nature who records what he sees and describes full and colorful characters. His intent is to acquaint his audience with the assortment of people he has meet.
I do not believe, based upon the manner Chaucer uses to tell the story, that he has any intent to lead anyone to a more righteous life. He is simply entertaining us with a slice of life in the Middle Ages.