The author uses the kids picking on Piggy to advance the themes by showing the breaking of order on the island. Jack and his choir are the people who make fun of Piggy the most, and Jack is the main representation of chaos, so the way the William Golding made Jack and the Choir slowly disobey Piggy and Ralph’s rules and break away from his tribe represented the order slowly leaving the island.
Even though Piggy has useful and great ideas for how to structure the island, most of the boys pick on him because of his weight, his asthma, and the lack of consequences if they do not follow his ideas. Most of the boys find him annoying, so when he tells them to do certain things they don't always listen and the Golding uses this to advance the themes of the novel by showing the breaking of order on the