Here's why:
* Luke's Motivation: Luke is driven by a deep-seated resentment towards the gods, stemming from a childhood tragedy involving his father, Hermes. He believes the gods are untrustworthy and seeks to overthrow them, believing that the world would be better off without their interference.
* Manipulating Events: Luke orchestrates the whole plot to frame Percy, using his knowledge of the Olympian world and his abilities as a powerful demigod. He plants evidence, manipulates Kronos (the Titan Lord), and even uses the power of a stolen magical item to amplify the accusations against Percy.
* Personal Connection: Luke's betrayal is made all the more poignant because he was a friend of Percy's at Camp Half-Blood, initially acting as a mentor figure. This creates a strong sense of personal betrayal for Percy and adds to the emotional impact of the story.
It's important to remember that Luke's actions are not simply a case of pure evil. He believes he is acting for the greater good, even if his methods are extreme and ultimately misguided.