This statement could mean that the nature of the villain in these novels is so extreme that there is no room for rehabilitation or alternative endings. The very essence of their character, which might involve excessive cruelty, greed, or a thirst for power, is so contrary to the values of the fictional world that death becomes the logical conclusion. For example, if a villain has committed heinous crimes like mass murder or tyranny, the narrative may not allow for any other form of resolution. This also reflects on the audience's expectations from such novels. They often anticipate the downfall of the villain, and death is the ultimate form of downfall in most fictional settings.
In the given search results, there were a few novels that were recommended by the villain. Among them," The Villains 'Group Pet Little Junior Sister " was an immortal cultivation novel. It told the story of the female protagonist, Yu Nianqing, who was schemed to become the little junior sister of the great devils, but became the villain's group pet. The novel was already finished. In addition, I'm a Villain was also a cultivation novel with villain elements, and it had been completed.
Often, the villain's actions against the protagonist and the general good lead to their death. They might have committed heinous crimes like murder or mass destruction, and the forces of justice in the novel ultimately bring about their downfall.
It simplifies the plot structure in a way. There is a clear end - goal for the villain's arc, which is death. So, the plot can be built around leading the villain towards that inevitable end. This might involve the protagonist's actions gradually cornering the villain.