One possible reason could be for his safety. Konoha is a well - protected village with many skilled ninja. She might believe that leaving him there would ensure he has the best chance at survival and growth as a ninja. Also, she may have some mission or obligation that forces her to leave him behind, perhaps something related to the greater good of the village or the ninja world in general.
Well, if Naruto and Kushina left Konoha in fanfiction, it would change a great deal. Naruto would not have the same relationships with his friends like Sasuke and Sakura. He might develop different fighting styles as he wouldn't be trained by the same people in Konoha. Kushina, being a strong kunoichi, could train Naruto in her own unique ways. And their departure could also cause a stir in Konoha, with some people trying to find them and others realizing the mistakes they made in how they treated Naruto and his family in the past.
The plot could develop in various ways. For one, Naruto's power growth might accelerate as he and Kushina explore different regions and learn new techniques. They could also encounter old enemies of the Uzumaki clan, which would add a new layer of conflict. Maybe they'd find a lost Uzumaki village and help revive it.
The fact that Naruto left Konoha has a profound impact on his son. Socially, he may be ostracized or at least eyed with suspicion. Emotionally, he might struggle with feelings of abandonment and yet also have a sense of pride in his father's courage to break away. In terms of his ninja training, he may lack the traditional support system of Konoha but could develop unique skills out of necessity. For instance, he might have to learn self - defense techniques on his own or seek out mentors from outside the village. This could lead to him having a very different fighting style compared to the typical Konoha ninjas.
Naruto might forgive Konoha because he realizes that holding a grudge won't solve anything. He has seen the destruction that hatred can cause, like during the Pain arc. So, he chooses to forgive in order to move forward and bring about positive change. Another reason could be his respect for the previous Hokages and their ideals for Konoha.
One possible reason could be fear. Naruto has the Nine - Tails within him, and some in Konoha might be too afraid of its power getting out of control. They may not fully trust Naruto to keep it in check.
Another reason might be that Naruto is seeking a greater purpose. In the fanfiction, his 'godlike' state could make him realize that there are threats out there that he can't face while being tied to Konoha. He may leave to protect the world on a larger scale, believing that he can be more effective away from the village.
One possible reason could be that Naruto discovers some dark secrets about the village leadership that go against his values. For example, if he finds out that they have been using underhanded means to maintain power.
Another reason could be that he witnesses corruption or unfairness within the village leadership. If he sees that the system is rigged against certain groups, including himself or his friends, he could grow to hate Konoha and decide to leave.
One possible reason could be that Naruto feels betrayed by Konoha. Maybe he discovers some dark secrets about the village that make him lose faith in it. For example, if he finds out that the village elders were involved in unethical experiments or plots against his friends or family, he might not want to help.