One possible reason could be a misinformation plot. Maybe in the fanfiction, Naruto has been led to believe that Yondaime had some dark secrets or did something bad to his family that he discovers later in the story.
It could be due to jealousy. Suppose in this fanfiction, Yondaime was always favored and Naruto felt neglected. So, over time, this feeling turned into hatred. For example, if Yondaime was given all the best training opportunities and Naruto was left with scraps, that would create resentment.
Perhaps Naruto blames Yondaime for his mother's death. In the original story, Kushina died while giving birth to Naruto, and if in this fanfiction there are some hidden motives or actions of Yondaime related to that event, Naruto could hold a grudge. Like if he found out that Yondaime could have saved Kushina but chose not to for some greater good that Naruto doesn't understand or accept.
Perhaps Naruto feels that the Hokage has been too strict or unfair in dealing with certain situations. Like if the Hokage didn't support Naruto's way of trying to bring peace and unity, which Naruto firmly believes in. This could lead to a growing resentment and eventually hatred.
One possible reason could be a feeling of betrayal. Maybe the Kages made decisions that Naruto thought were against the greater good or the well - being of the ninja world. For example, if they were too focused on protecting their own villages at the expense of others.
Perhaps he blames ninjas in general for the loss of someone close to him. For example, if a group of rogue ninjas were responsible for the death of a dear friend or family member, it could make him resent the whole ninja concept. He might think that if there were no ninjas, such tragedies wouldn't occur.
One possible reason could be betrayal. If Naruto was constantly let down or betrayed by those he trusted among humans, it could lead to his hatred. For example, if his friends turned on him because of his jinchuriki status.
One possible reason could be a misunderstanding. Maybe Anko was involved in a mission that Naruto thought was unjust, and he misjudged her actions as being malicious. For example, if she had to capture someone Naruto considered a friend, even if it was for the right reasons from Anko's perspective, Naruto might hold a grudge.
Perhaps in this fanfiction, Naruto has been influenced by some external force. It could be a dark entity that has corrupted his view of Team 7. He might see them as a hindrance to achieving some greater, more self - centered objective. Also, it could be that Naruto has had some sort of personal revelation about his past and blames Team 7, or certain members of it, for things that he now believes held him back in the past.
Maybe in this fanfiction, there was some sort of dark magic or mind - control involved. Kushina could have been unknowingly influenced to do something that deeply hurt Naruto. Like she was made to abandon Naruto at a crucial moment in his life, which then led to his hatred.
One possible reason could be a misinterpretation of Kushina's actions. Maybe some events were presented in a way that made Naruto think she was neglectful or had made bad decisions in the past.
One possible reason could be that in the fanfic, Jiraiya might have made a decision that Naruto strongly disagreed with, like leaving him alone at a crucial time for a long mission. This could make Naruto feel abandoned and thus start to hate him.