Maybe Harry has faced so many traumas and disappointments in the wizarding world that he just decides to distance himself from all the chaos. For example, he might be tired of the constant battles against the Dark Arts and the politics within Hogwarts and the Ministry. He could stop caring about his reputation as 'the Chosen One' and simply want to live a quiet life, away from the spotlight and the expectations.
In the 'harry potter stops caring fanfic', it could be that Harry has lost too many friends or loved ones. This extreme grief makes him numb and he no longer has the energy to care about the things he used to. He might stop attending classes, stop participating in Quidditch, and just isolate himself in the Room of Requirement. He doesn't care about grades or winning any more, just lost in his own sorrow.
It could be a situation where Harry discovers some dark secrets about the wizarding world that make him lose faith in it all. He might find out that some of the respected institutions or people he once looked up to are involved in unethical or immoral activities. So he stops caring about upholding the values of the wizarding world and decides to go his own way, perhaps exploring a more neutral or even a Muggle - like existence.
One possible reason could be that he has been through so much in his original adventures that he's just tired. He might feel like he's constantly being put in new, often contrived, situations in the fanfiction and he simply wants to step away from all the chaos and drama.
One possible reason could be that Naruto has faced too many betrayals. Maybe his friends turned on him in the fanfic, which made him lose faith and stop caring.
Well, it could start with Harry gradually noticing how the fanfiction world is not in line with his own values or experiences. For instance, he might find that the magic system is misrepresented in a way that he can't accept.
Well, perhaps it could be that Stiles has faced so many difficult situations in the original story that he just reaches a breaking point and decides to stop caring about the things that used to bother him. Maybe he stops caring about the supernatural threats in his town, and this could lead to a series of events where his friends have to try and bring back the old Stiles.
One possible reason could be that Naruto has faced so many betrayals and hardships in the fanfiction. For example, if his friends turned on him for some contrived reasons, it might lead him to stop caring. Another reason could be the constant failure in achieving his goals, like protecting the village but always being undermined by political intrigue within the fan - made story.
One possible reason could be that Naruto realizes Sakura's unrequited love for Sasuke. He might feel tired of always being in a one - sided emotional situation with her. Another reason could be that Naruto has his own goals and growth to focus on. His journey to become Hokage and protect the village requires all his attention, leaving little room for his previous feelings for Sakura.
Dumbledore would also be affected. As a mentor - like figure to Harry, he has certain expectations and plans for Harry. If Harry stops caring, Dumbledore's grand schemes against Voldemort might be derailed. He would have to find a new way to motivate Harry or adjust his strategies.
Well, perhaps Harry could use his magic skills like the Patronus charm to hold Loki at bay. Since Harry has experience dealing with dark forces, he might be able to outwit Loki's trickery.
Perhaps Harry has grown tired of always following Dumbledore's instructions without fully understanding the reasons behind them. He might want to make his own decisions and take control of his own destiny, rather than relying on Dumbledore all the time.
One possible reason could be that Naruto has finally realized that Sakura's heart has always been with Sasuke. After years of chasing after her and getting constantly rejected or overlooked, he just gets tired and decides to move on. He might start to focus more on his own personal growth and the other relationships in his life that are more reciprocal.