Perhaps Naruto with the Rinnegan has seen a darker side of Konoha that he was previously unaware of. It could be something related to the village's past secrets, such as hidden experiments or unjust actions towards other ninja clans. This new knowledge makes him so disillusioned that he refuses to offer his help. Also, he might have formed new alliances outside of Konoha that he values more and that conflict with Konoha's interests.
It could also be that Naruto has grown disillusioned with the politics in Konoha. Constant power struggles, nepotism, or unfair treatment of certain groups within the village might have pushed him away. He might feel that his help would only be enabling a corrupt system.
Perhaps Naruto has found a new purpose or community outside of Konoha that values him more. He may be so content with his new life that he simply doesn't want to get involved with Konoha's problems anymore. Konoha's actions towards him could have made him realize that his loyalty was misplaced all along.
One possible reason could be that Naruto feels betrayed by Konoha. Maybe he discovers some dark secrets about the village's leadership or past actions that make him question whether Konoha is truly worth saving. For example, if he finds out that they were involved in unethical experiments or unjust treatment of certain clans. Another reason might be that he has been pushed too far by the villagers' continuous mistrust and discrimination towards him, despite all he has done for them. So he decides he's had enough and refuses to save the village that has not fully accepted him.
Perhaps Naruto has been pushed too far by the villagers' continuous mistreatment. Even though he has saved them multiple times, they still show hostility or indifference towards him. So, in the fanfiction, he decides not to help Konoha anymore as a form of self - protection and to break free from this one - sided relationship.
One possible reason could be that Naruto feels betrayed by Konoha. Maybe he discovers some dark secrets about the village that make him question whether it's worth protecting. For example, if he finds out that the village elders were involved in unethical experiments or unjust actions against certain groups. Another reason might be that Naruto has different ideals now. He could believe that there are more important things in the world than just protecting Konoha, like bringing true peace to all nations without focusing on one village's interests.
One possible reason could be past betrayals. Maybe he was mistreated by the village in some way, like being blamed for things he didn't do or not getting the support he needed when he was younger. So he feels no obligation to help.
Another reason might be that he has some internal conflict. For example, he could be doubting the purpose of the training. If he doesn't see a clear goal or if he's starting to question the methods, he might refuse. In some fanfics, he could also be influenced by new friends or ideas that make him question the traditional ninja training regime.
One possible reason could be that he's tired of being used by the British wizarding world. He has faced so many challenges and been through a great deal of trauma, like fighting Voldemort multiple times. He might feel that it's time for others to take responsibility and that he wants to focus on his own life for a change.
Another reason could be related to his personal goals. Naruto might have something else in mind that he believes is more important than taking the Chunin Exams at that moment. For example, he could be focused on finding out more about his family or some mystery in the village. He may also not want to participate because he doesn't want to be part of the traditional system that he might view as unfair or too rigid. He's always been a bit of an outlier, and the Chunin Exams represent a very structured and competitive event that might not appeal to his free - spirited nature.
One possible reason could be his loyalty to his own village and friends in the Naruto world. He has strong bonds there and wouldn't easily abandon them to join someone in a different fictional context like Rias. Another reason might be the difference in values. Naruto values hard work, friendship, and the will of fire, while Rias's group may have different goals and values that Naruto doesn't align with.