Why does the king in "The Tortoise with a Pretty Daughter" make the law about daughters?

The King had given his son fifty young girls as his wives. But he liked none of them. The king got very angry at this and in his anger made a law that whoever in the country had a daughter finer than his son's wives, he along with the daughter and daughter's mother would be killed.

Explanation:

"The Tortoise with a Pretty Daughter" is a Nigerian folktale. The Tortoise' wife wants their beautiful daughter to be killed lest they all be killed by the king. But the Tortoise himself is against this and keeps his daughter hidden. After some twists the prince finds the daughter and fall in love with her at once. The king initially very angry but on seeing the girls' beauty decides to change the law and marries his son the girl.