Here's why:
* The tale is a satire: It's meant to poke fun at human nature, particularly the follies of love, marriage, and social hierarchy. No character is presented as wholly virtuous or successful.
* All characters are flawed: Nicholas, the student, is clever but manipulative and lustful. Absolon, the parish clerk, is foolishly in love and easily tricked. Alison, the young wife, is attractive but fickle and prone to deceit. John, the old carpenter, is gullible and easily fooled.
* The story ends with chaos and confusion: Nicholas escapes with his life, but his scheme backfires spectacularly. Absolon gets tricked and humiliated. John is left to face the consequences of his wife's infidelity.
Ultimately, the story is meant to be enjoyed for its humor and satire, not for its clear-cut resolution.