Here's why:
* Cronus's Role: Cronus is the father of Zeus and the leader of the Titans, who were overthrown by the Olympian Gods. His story is mostly relevant to the Greek myths surrounding the creation of the world and the rise of the Olympians.
* The Lightning Thief's Focus: The Lightning Thief focuses on Percy Jackson's journey to clear his name and find the missing lightning bolt. The story primarily deals with the conflict between Zeus and Hades, along with the threat of the monsters that threaten the mortal world.
While Cronus is a significant figure in Greek mythology, his story is not directly relevant to the events of The Lightning Thief.