King Arthur was ready to punish the knight according to the law, but the queen and the other ladies begged him not to kill him. According to the law, the knight was to lose his head given his crime and the interest it generated. Luckily for the Knight, King Arthur complied with his wife’s request and instead handed the knight to her to do as she pleased.
But then the queen and other ladies too prayed so long that the king might grant him grace,
King Arthur spared him for at least a space; He left him to the queen to do her will...
The king might have read the mood of the women around him and decided to allow them to deliver the appropriate punishment to the knight. His decision would definitely calm them down and also work to secure their continued support. Thus, the king’s decision might have been politically motivated. The king might also have wanted to express his personal beliefs about women’s roles in his kingdom by extending them some level of autonomy in the public matter.
In “The Wife of Bath’s Tale", there are several reasons why King Arthur might have allowed the queen to punish the knight. One reason is that the knight raped a young woman, and therefore, the women were very upset. Allowing a woman to decide his punishment might be an effective way of calming the female citizens of his kingdom.
Another reason he might have allowed her to decide the punishment is that perhaps a woman’s punishment might be more humiliating for him, and he certainly deserves it. The knight goes off on his quest to find what women want, and he cannot even find the answer. When he does find the answer, that all women want dominion over their husbands, he then has to stand up and report that to the entire court.
Of course, if you asked the Wife of Bath why the queen was allowed to punish the knight, she would have a different opinion altogether. King Arthur was an ideal king; it is a given that he always did the right thing. As the theme of the story is that women should have power over their men, it is likely that King Arthur allowed Guinevere the power to show that he understood women should have power.