Another reason might be related to his pursuit of power. In the fanfic, if he delved too deep into a dangerous form of power - seeking that corrupted his mind. He might see himself as a threat to those he loves and decide that the only way to keep them safe is by taking his own life.
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 extreme guilt. Maybe he fails to protect his friends in a major battle and feels so responsible that he can't bear it. For example, if Sasuke were to die because Naruto couldn't reach him in time, Naruto might sink into such deep guilt that he sees no way out but death.
In this kind of fanfic, one possible reason could be unrequited love. Naruto might have felt so hopeless about his feelings for Sakura never being returned that he saw no way out. He had always been in love with her, and if she continuously rejected him and perhaps even chose someone else, it could have broken his spirit to the point of self - destruction.
One possible reason could be his childhood as an outcast. Growing up without parents and being shunned by some in the village made him feel like he didn't belong. This could have led to his low self - esteem. Another reason might be his struggles in school. Naruto wasn't exactly a star student at the ninja academy, and constantly being compared to his peers in a negative way could have made him think less of himself.
There are several reasons. He might be afraid of getting too close to people because he's lost someone important and is scared of more loss. It could also be that he's discovered some new power within himself that he doesn't understand and is worried about hurting others if he gets too involved. Additionally, there could be some political intrigue in the village. Maybe there are some people who are plotting against him and he's keeping to himself to avoid being a target or putting others in danger.
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 reason could be the loss of his friends. Naruto values his friends deeply, and if he were to lose someone like Sasuke again, it would be devastating. Another reason might be the pressure of being the Hokage. The responsibilities are huge, and he might feel like he's not living up to the expectations of the village. Also, memories of his lonely childhood could resurface, making him feel sad and alone, leading to him crying himself to sleep.
Some creators might want to explore a darker side of Naruto's character. Maybe they're tired of the always - positive and heroic Naruto and want to see what he'd be like if pushed to the extreme.
Some people might create it just for shock value. They want to get a reaction from the Naruto fan community by presenting such a radical and against - the - norm idea.
Maybe in the fanfic, Death is not a traditional Grim Reaper - like figure but rather a form of an evil curse that has been plaguing the ninja world. Naruto, being the hero, is the only one with enough positive energy and determination to face it. He could start by gathering allies who have also been affected by this 'Death' curse. Together, they form a plan. Naruto would be the vanguard, using his speed and strength to break through the defenses of the curse - based Death and then use his willpower to shatter it completely.
Maybe some writers want to explore extreme character deviations. They might be interested in creating a shock factor by making a beloved character like Ahsoka do something so heinous. It could also be an attempt to explore a very dark, alternate universe where all the good characters turn bad.