Short Answer: Because it wanted to catch the bookworm burglars! 📚🐛👮♂️
Explanation: The book decided to join the police force because it had heard that there were mischievous bookworm burglars on the loose! It couldn't bear the thought of its fellow books being devoured by these notorious worms, so it bravely took up the badge and vowed to protect its literary companions. With a sense of duty and a dash of humor, this book-turned-officer set out on a mission to catch those wily bookworms and bring them to justice. 📖💪🚓