Why did Erin Hunter make firestar die?

Erin Hunter chose to have Firestar die to bring closure to his character arc and to emphasize the themes of sacrifice and the cyclical nature of life in the "Warriors" series. His death allows for the passing of leadership to a new generation and highlights the consequences of ongoing conflicts within the clans. Additionally, it serves to deepen the emotional impact of the story, reinforcing the idea that every leader must face their mortality.