One possible reason could be a series of misunderstandings. Maybe his family made decisions that he felt were against his principles or dreams, and after repeated attempts to reconcile the differences, he just lost hope. For example, if his family was against his ninja way, which is such a core part of his identity.
One reason could be the constant setbacks he faces. He might feel that no matter how hard he tries, he can't achieve his goal. For example, if he fails too many times in battles against strong opponents, he could lose hope. Another reason might be the loss of important people in his life. If someone like Iruka or Kakashi, who have been his pillars of support, were to die, it could shatter his dreams as they are so closely tied to his will to succeed for their sake.
It could also be that he is tired of the false expectations created by fanfiction. In fanfiction, his character might be portrayed in ways that don't match who he really is. He wants to be true to himself and his ninja way, so he gives up fanfiction.
One reason could be the overwhelming pressure. Being Hokage means shouldering the safety and well - being of the entire village. Naruto might have realized that he can't bear that kind of stress forever. Another factor could be personal sacrifice. He may have seen how being Hokage has cost others in their personal lives and he doesn't want to go through the same. Also, he might have new dreams or goals that are not compatible with the role of Hokage, like exploring the world outside the village more freely.
It could also be due to a misunderstanding. Some false information might have spread in the fanfic's world, making Naruto believe that everyone has turned their backs on him. Like, some bad guys framed his friends, and Naruto, being unable to see through the lies at first, gives up on everyone in despair.
One reason could be the sacrifices he has to make for the village. Naruto is so dedicated to protecting Konoha that he might feel he doesn't have time for love. His responsibilities as Hokage are immense, and he has to constantly be on guard against threats. Another reason could be past traumas. He has lost many people he cared about, like Jiraiya. This could make him afraid of getting close to someone again and losing them, so he gives up on love.
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.
Another factor could be the nature of his ninja life. It's full of uncertainties and risks. He may worry that if he falls in love, his loved one could become a target for his enemies. Naruto has made many enemies over the years, and he wouldn't want to put someone he loves in danger, so he decides to give up on love.
One possible reason could be a lack of time. Maybe Ash has become too busy with other aspects of life, like work or studies, and can't find the time to write fanfiction anymore.
Perhaps he simply lost his creative inspiration. Fanfiction writing often requires a constant flow of new ideas, and if he's been through a lot of stress or has had some personal issues, like his complex relationship with Lily still haunting him, it could dry up his well of creativity.
It could be due to a physical or mental injury. If Naruto got seriously injured during the Chunin Exam, and he didn't think he could recover in time to compete effectively, he might give up. Mentally, if he was somehow affected by a genjutsu that made him lose his confidence or will to fight, that could also lead to his decision to give up.