Perhaps the themes are too different. Naruto often deals with themes like friendship, but also has a strong undercurrent of revenge and redemption. Fairy Tail is mainly about the power of friendship and family within the guild. Writers may find it difficult to merge these two different thematic focuses, so they choose to keep Naruto out of their Fairy Tail fanfictions.
It might be due to the fanbase loyalty. Fairy Tail fans are really into their own world and characters. They might not want to introduce Naruto elements as they feel it could disrupt the original charm of Fairy Tail. Also, the art styles are different. Naruto has a more traditional Japanese anime look, and Fairy Tail has its own style. This visual difference could be a reason for the lack of crossovers in fanfictions.
One possible reason could be a conflict of power. Naruto has his own set of powers from the Naruto universe, like chakra and jutsus. In Fairy Tail, magic is the main power source. Maybe his powers were seen as a threat or too different, causing the guild to force him out. For example, if his chakra-based attacks were disrupting the magical balance in Fairy Tail's world.
Maybe it's due to power differences. Naruto has his own set of unique and powerful jutsu. In the Fairy Tail universe, magic is the main form of power. He could feel that his powers are not being utilized or respected in the right way. He might also be frustrated with the lack of understanding of his ninja skills among the Fairy Tail members, so he chooses to leave.
In the fanfiction, there could be a family curse or some sort of obligation that forces his family to keep their distance from Naruto. They might believe that by ignoring him, they are protecting him or the family as a whole. For instance, if there is a dark force targeting Naruto, they might think that acting as if they don't care will keep him safe from that threat.
One possible reason is the difference in power systems. Naruto has its chakra - based ninja abilities, while Fairy Tail has magic. Combining them in fanfiction might seem forced and not make logical sense to fans of Naruto.
The writer could focus on the similarities in the themes. Both Naruto and Fairy Tail have friendship as a major theme. So, a fanfiction could start with a Naruto character who values friendship in a similar way as Fairy Tail characters. They could meet and form a bond based on this shared value. Also, using side characters from both series could be easier than main characters. For instance, some of the less prominent ninja from Naruto could interact with Fairy Tail's secondary characters more smoothly.
One possible reason could be that Kakashi is preoccupied with other important matters in the village. Maybe he has some top - secret missions or tasks assigned by the Hokage that demand his full attention, leaving him with little time to focus on Naruto.
Maybe she just lost interest in the Fairy Tail world. Fanfiction can be a passing fancy, and her enthusiasm might have waned over time.
Another reason could be related to his past. Maybe he has a dark secret from his past that he's afraid will be revealed. In Fairy Tail, where people are generally open and honest, the fear of being exposed and shunned because of this secret could be overwhelming. This could make him feel that the only way out is to end his life.
One possible reason could be jealousy. Maybe some members of Team 7 are jealous of Naruto's natural talent that he doesn't even realize he has. Another reason might be a misunderstanding. Naruto is often brash and loud, and his teammates could misinterpret this as him being over - confident or show - offish, when in reality he's just trying to prove himself. Also, there could be a pre - existing bias. If some members of Team 7 come from more 'privileged' ninja families, they might look down on Naruto who was an outcast in the village for a long time.
Another reason might be related to Naruto's loyalty being questioned. In fanfiction, there could be a plot where an enemy tricks the guild into believing Naruto has betrayed them. The Fairy Tail guild values loyalty highly, and if they think Naruto has sided with an enemy, they might banish him. For example, if an enemy uses some sort of illusion magic to make it seem like Naruto has attacked a guild member, this could lead to his banishment.