why did they kill joel

Joel was killed by Abby in "The Last of Us" because Joel had previously killed Abby's father, who was the chief doctor of the Fireflies. Joel had slaughtered the Fireflies' crew to save Ellie, who was going to be sacrificed for a cure to the infection. Abby sought revenge for her father's death and brutally killed Joel with a golf club in the early part of Season 2 to avenge her father. Joel’s death was a pivotal inciting incident in the story, designed to set the stage for the themes of revenge, cycle of violence, and redemption explored in the series. Abby's act reflects the deep emotional trauma and the drive for vengeance that the loss of a loved one can provoke, linking their stories together in a complex narrative of consequence and pain.