In the fanfiction, it could be that Naruto is ostracized by the very people he has been trying to protect. The villagers' distrust and fear of his power could resurface, making him feel isolated and alone. He might think that if the people he's fighting for don't want him, there's no point in living. This sense of abandonment could drive him to give up on life.
Perhaps in this fanfiction, Naruto discovers some dark secrets about his past, like his father being the one who caused some great harm to the village in the past. This revelation could shatter his self - identity and make him lose hope. Also, if he fails to protect the village from a major threat despite his best efforts, it could lead him to give up, thinking he's not good enough.
One possible reason could be the overwhelming loss he has faced. He's lost many dear friends and mentors throughout his journey. For example, when Jiraiya died, it was a huge blow to him. Another reason might be the constant pressure of being the savior of the village. The weight of everyone's expectations could lead him to feel so tired and defeated that he gives up on life.
One possible reason could be that Naruto realizes Sasuke is too far gone on his dark path. After numerous attempts to bring him back, Naruto might start to think that Sasuke doesn't want to be saved. He may see that Sasuke's actions are causing too much harm to the village and the people he loves, and Naruto has to prioritize them over Sasuke. So, he gives up on the idea of bringing Sasuke back.
Another reason might be related to Naruto's growth in the fanfiction. If Naruto becomes too powerful or changes in a way that Hinata no longer feels connected to him, she could give up. Suppose Naruto starts to embrace a more solitary and power - hungry path, which goes against Hinata's values of family and connection. This divergence in their paths could cause her to lose hope in their relationship and give up on him.
One possible reason could be pure creativity and the desire to break boundaries. Writers might want to explore a completely different side of Naruto that is not shown in the original series. It could also be a way to shock the readers and get their attention.
One possible reason could be differences in their future goals. Naruto is highly focused on being Hokage and protecting the village, while Hinata might want a more peaceful, family - centered life. Maybe Naruto's hectic schedule and constant danger make Hinata feel neglected, leading to their break - up.
One possible reason could be to gain extraordinary powers. In some fanfictions, giving up humanity might be a sacrifice for a greater magical ability, like being able to control all elements or access a new level of magic that is otherwise inaccessible to humans.
One possible reason could be that Naruto realizes Sasuke is too far gone in his quest for revenge. Naruto might see that no matter how much he tries, Sasuke won't change his ways, so he gives up. For example, if Sasuke keeps attacking innocent people in his pursuit of power to defeat Itachi's enemies, Naruto might finally lose hope.
One possible reason could be that he experiences a great loss, like the death of a dear friend. This might shatter his confidence and make him lose his passion for being a ninja.
Perhaps the fanfiction keeps rehashing the same tired storylines about Konoha. Naruto might be tired of seeing the same things over and over again, like always focusing on the village's dark secrets in a clichéd way instead of exploring new aspects of Konoha and its people.
One reason could be some sort of betrayal he feels. Maybe he discovers a secret that makes him think Team 7 was never truly his team. For example, if he found out that the village leaders had some ulterior motives for forming the team that involved using him.
Perhaps it's a training exercise that gets out of hand. In the world of Naruto, intense training often mimics real battles. If they were sparring and emotions ran high, it could turn into a full - fledged fight. Also, Sakura might be trying to prove herself to Naruto, and Naruto, not understanding her intentions, might respond aggressively.