Why does Chaucer place the Pardoner towards the end of the Prologue?
He is perhaps the most controversial character in the tale. He has a low-life job that stems off of his greed. After giving a sermon he sells bogus relics. His reason for going on this pilgrimmage was to con people. Ironically, even after his tale against greed, he tries to sell the other pilgrims his relics. Chaucer places the characters in his tale from the highest and most respected to the lowest and insolent. For this reason, the Pardoner finishes out the Prologue.
Why did Chaucer include so few actually "good" people in his tale?
When Chaucer wrote Canterbury Tales, he was trying to represent medieval society. Each person symbolizes a social class. There a very few people in the world that we could call "good" in nature. For this reason, the only people in this tale with the right morals are the knight, the parson, and the plowman. They are the few "good" men in society.