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.
The villagers' attitude towards Naruto would shift. They have come to see Naruto as a symbol of hope and a powerful ninja. If he gives up, some might be disappointed, while others who were always a bit jealous or suspicious of him might feel vindicated. His friends among the villagers, like Shikamaru or Choji, would be sad to see him go from the ninja life but would still try to maintain their friendship with him in a different context.
One possible reason could be that he experiences a great personal loss. Maybe he loses someone very dear to him during a mission, like his best friend or a respected mentor. This loss makes him question the whole ninja life and all the violence and danger it entails, leading him to give it up.
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.
With his friends, it might create a sense of shock. His friends who have always supported his dream of being Hokage would be surprised. Some might be disappointed, like Sakura who has seen Naruto's growth towards that goal. But others, like Shikamaru, might understand his decision and still support him in whatever he chooses to do. With his family, if he has a family at this point, it could bring a sense of relief as they may not want him to be in such a dangerous and stressful position.
It could be that Naruto has other creative or intellectual interests. For example, he might be more interested in art or learning about the history of the ninja villages rather than participating in ninja battles. He could find the rigid ninja training and the constant competition unappealing. Also, perhaps he has a different sense of purpose, like wanting to focus on building peace in a non - combat way, which doesn't require being a ninja in the traditional sense.
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.
In some cases, the fanfiction might be a crossover with another universe where the idea of a ninja doesn't fit. So, to make Naruto fit into this new universe, the writer has to take away his ninja identity. This allows for new and interesting interactions between Naruto and characters from the other universe.
Some fans might be disappointed. Fanfiction often allows them to explore different scenarios with Naruto's character. If he gives it up, it's like closing a door on those creative possibilities.