Perhaps there is a misunderstanding within the family. His siblings might be misinterpreted as more in need of attention or resources. Naruto, on the other hand, is seen as more self - sufficient, even if that's not the case. So, the family ends up focusing on the siblings while neglecting Naruto without really realizing his true situation.
One reason could be that his siblings have some special abilities or talents that overshadow Naruto. In the ninja world, those with unique powers often get more attention. So, if his siblings possess something extraordinary, Naruto might be pushed to the side.
One possible reason could be that they are too involved in their own shinobi duties. The world of ninjas is full of dangerous missions, and they might be constantly away on important tasks, leaving Naruto feeling neglected.
Maybe there are secrets in the family. For example, his parents might be involved in some dangerous and secretive missions that require them to keep their distance from Naruto to protect him, but Naruto misinterprets it as neglect.
Maybe he's been influenced by someone who has a different view of heritage. For example, if he meets a character who believes that one should create their own identity rather than relying on heritage, Naruto could be swayed. Another possibility is that he has some sort of resentment towards his heritage. Perhaps there are things in his family's past or in the traditions associated with his heritage that he doesn't agree with or is ashamed of.
It could also be due to some family curse or prophecy. In the Naruto universe, there are often strange powers and curses. Maybe there was a prophecy that said Naruto's family had to keep their distance from him to protect him from some greater evil. So, they chose to neglect him in order to keep him safe, even if it was a difficult choice.
He might try to prove himself. Naruto has always been a determined character. So, he would likely focus on his training more, aiming to show his worth to those who neglect him. For example, he could strive to become a stronger ninja faster than his siblings, in the hope that his efforts would be noticed and the neglect would stop.
One possible reason could be that they are too focused on their own problems or duties. Maybe they are involved in some important shinobi business that takes up all their time and attention, causing them to overlook Naruto.
One possible reason could be jealousy. If Naruto has the rare Mokuton ability, his family might be jealous of his potential power and neglect him out of spite.
Perhaps he's been influenced by someone who gives him bad advice. For example, if someone tells him that natural talent is enough and training is overrated. Also, he could be dealing with some personal problems, like a conflict within his family or among his friends that takes up all his time and mental energy, causing him to neglect training.
In the fanfic, Kakashi might neglect Naruto's training due to a variety of reasons. He could be preoccupied with his own research or a secret mission that demands his full attention. There could also be a misunderstanding between him and Naruto. Maybe Naruto has done something that Kakashi misinterprets, causing him to distance himself from Naruto's training. Additionally, the fanfic could introduce new characters or plot elements that draw Kakashi's focus away from Naruto. For example, a new threat to the village that Kakashi feels he must handle alone, thus neglecting his duties as Naruto's trainer.
He might try to prove himself. Naruto has always been a determined character. He could focus on his ninja training more intently, aiming to show everyone his worth despite being neglected. Maybe he'd also start to distance himself a bit from his family situation and form closer bonds with his friends like Sasuke and Sakura, who might understand and support him through this tough time.