Why does ryuk leave light?

Ryuk ultimately leaves Light Yagami because he becomes disillusioned with Light's increasingly ruthless and dictatorial behavior. As Light's actions grow more extreme and morally questionable, Ryuk, who is primarily interested in observing human nature and the chaos that the Death Note brings, realizes that Light has strayed too far from the game that intrigued him. Additionally, Ryuk has no personal investment in Light's success or failure; he merely enjoys the entertainment and decides to move on when it no longer amuses him.