Why Am I the Villain of the System?

Why did I become a villain in time travel and let me go against the protagonist? Was it because I was afraid that my death would not be miserable enough? Emperor: "If you want to die, just dream." Demon King: "You are not allowed to leave me without my permission." General: "Don't worry, I will definitely cure you." Su Qian: "I just want to play games happily, why do I have to die in the end?"