Here's why Luke does it:
* He's manipulated by Kronos: Luke is a demigod son of Hermes, and he was kidnapped by Kronos when he was a baby. Kronos, the Titan who was overthrown by the Olympians, has been working in the shadows to regain his power. He's been manipulating Luke into doing his bidding, making him believe that the Olympians are evil and that he's destined for greatness.
* He thinks he's helping: Kronos convinces Luke that the only way to defeat the Olympians is to take the master bolt and start a war. Luke, who is bitter and angry at the gods for abandoning him and his mother, believes that this is the only way to bring about a new order.
* He's seeking revenge: Luke is driven by a deep desire for revenge against the Olympians, who he believes wronged him. He believes that by stealing the master bolt, he can finally strike a blow against them and prove his worth.
It's important to note that Luke is not inherently evil. He is a complex character who has been manipulated and influenced by Kronos. He is a victim of circumstance, and his actions are driven by a desire for justice and a sense of betrayal.