Another reason could be that Naruto is lured away by an external force. Some powerful figure or group might convince him that leaving his parents is for the greater good, perhaps in the name of protecting them or the village in a more effective way.
Naruto's departure from his parents may initially cause him to be more reckless as he tries to prove himself without their guidance. However, over time, he could learn to be more cautious and calculated. This change in behavior would be a significant part of his character development, as he transitions from a somewhat naive boy to a more mature and self - reliant ninja.
Emotionally, Naruto would have to deal with a whole new set of family relationships. He grew up without his parents, and now having them back would be a huge adjustment. He might struggle to fit into a 'normal' family dynamic, and there could be some friction as they all get to know each other again.
In some fanfictions, Naruto might find a super - powerful jutsu or artifact. For example, he could discover a long - lost forbidden jutsu that has the power to bring the dead back to life. Or perhaps he stumbles upon a magical item during one of his adventures that is said to be able to revive the deceased.
On a personal level, Naruto would finally get the family he always wanted. But it might also bring some confusion and adjustment issues. His parents would be from a different time, and they'd need to adapt to the new world Naruto lives in. For example, they might be shocked by the new technology and the changes in ninja warfare.
One possible scenario could be that Harry leaves his parents due to a mysterious prophecy that he needs to fulfill away from them to keep them safe. Another could be that he discovers a hidden power within himself that he can't develop while staying with his parents, so he decides to leave.
Voldemort could still be the main antagonist. Even if Harry leaves his parents early, Voldemort might be hunting for him due to the prophecy. His dark presence would be a constant threat, driving Harry's actions and the plot of the fanfiction.
Iruka could play a role. He was Naruto's first teacher who believed in him. He might have some small piece of information that starts Naruto on his journey to find his parents. Then there's Tsunade. As the Hokage, she has access to a lot of secret files. She could either be an obstacle, not wanting Naruto to dig too deep, or she could be a helper, providing him with crucial information. And of course, the Nine - Tailed Fox. It was sealed inside Naruto by his father, so it might have some memories or knowledge related to Naruto's parents that it could share with Naruto.
He might meet other wandering ninjas who are also on a quest for power or knowledge. They could either become his allies or foes depending on their motives.
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.