One possible reason could be mind control. Maybe an enemy uses a powerful genjutsu on Naruto, making him lose control and attack the villagers. For example, Orochimaru might have a new jutsu to manipulate Naruto's mind for his own evil purposes.
Another reason might be a curse. There could be an ancient curse placed on Naruto that causes him to go berserk and attack the villagers. This curse could be related to the Nine - Tails within him, perhaps some dark magic from the past that gets triggered and makes him lose his rationality.
One possible reason could be fear. The villagers might be afraid of Naruto because of the Nine - Tailed Fox sealed within him. They see him as a potential threat and lash out in their fear. Another reason could be jealousy. Naruto is a powerful ninja in the making, and some villagers, who are not as strong or talented, might take out their insecurities on him.
One possible reason could be fear. Naruto has the Nine - Tails inside him, and the villagers might be so afraid of the power of the Nine - Tails getting out of control that they decide to take extreme measures. They might see Naruto not as a person but as a potential threat that needs to be eliminated.
Maybe for shock value. Some writers want to create a story that stands out and goes against the norm. By having Naruto kill villagers, it's a huge deviation from the original story and can grab readers' attention.
One possible plot twist could be that Naruto discovers one of the villagers was being controlled by a hidden enemy. This enemy could be using the villager's fear and hatred of Naruto to try and get rid of him. Another could be that Naruto's near - death experience makes the villagers realize their mistake and they start to protect him instead, leading to a change in the whole village - ninja relationship in the story.
One reason could be years of built - up resentment. The villagers have treated Naruto poorly for so long, constantly shunning him and making him feel like an outcast. In fanfiction, this could reach a boiling point where he just snaps. For example, if someone in the village made a particularly cruel comment about his parents, it might be the last straw.
One possible reason could be the way the villagers treated him as a child. They ostracized him because he was the host of the Nine - Tails. He was often alone and looked at with fear and disdain, which could have gradually built up his hatred.
It could also be due to a sense of isolation. If all his friends turned against him for some reason, perhaps being wrongly accused of a heinous crime. Naruto, who values his bonds deeply, might find such a situation unbearable and choose to end his own life.
One possible reason could be that Naruto feels betrayed by the village. Maybe he discovers some dark secrets about Konoha that make him lose faith in it. For example, if he finds out that the village leaders have been using him all along without truly caring for his well - being.
One possible reason could be that he's framed for a crime he didn't commit. Maybe someone powerful wants to get rid of him and plants false evidence. For example, they could make it seem like he attacked a village ally when in fact he was defending it from a hidden enemy.
It could be that Naruto has an epiphany about love and friendship. He might realize that his love for Sakura was more of an infatuation based on their childhood experiences. As he matures, he understands that true love should be mutual and free. So, he decides to let go of Sakura to find a relationship where his feelings are reciprocated, and also to respect Sakura's own choices.