One reason could be the extreme hardships the characters face in the original story. For example, Harry has lost his parents, faced Voldemort numerous times, and seen many friends die. In fanfiction, this could be amplified to a point where a character feels they have no will to live. Another aspect could be related to the sense of isolation. Some characters, like Snape, were always sort of alone in their struggles, and in fanfiction, this could lead to a loss of the will to live.
In the world of Harry Potter, the dark magic and the constant threat of death can be overwhelming. Fanfiction authors might explore how this could break a character's spirit. If a character is constantly under the influence of a dark curse or has been through a series of traumatic events related to dark magic, they may lose their will to live. Also, the social hierarchy in the wizarding world, such as the discrimination against Muggle - borns, can cause great distress to characters, which could be a factor in the 'no will to live' theme in fanfiction.
In the fanfiction, Harry Potter might live by himself because he is tired of the spotlight. After being in the public eye for so long, he desires a private life. He may also feel that living alone allows him to better understand himself and his powers. It could be that he has a prophecy or a personal quest that requires solitude. For example, he might be trying to master a very difficult and dangerous spell that he doesn't want anyone else to be in danger from if something goes wrong. Also, he could be exploring some dark corners of magic that the wizarding world might not approve of, and living alone gives him the freedom to do so without judgment.
One possible reason could be the overwhelming burden of his destiny. Constantly facing dark forces and the pressure of saving the wizarding world might have worn him down. Another reason could be the loss of his loved ones. For example, if in the fanfiction Hermione or Ron were killed, that could shatter his spirit.
One possible reason could be the continuous loss of his loved ones. In the original series, Harry has already endured so much pain from losing Sirius, Dumbledore, etc. In the fanfiction, perhaps there are additional deaths or betrayals that push him over the edge. Another reason might be the overwhelming burden of being 'the Chosen One'. The constant expectation to save the wizarding world could finally break him.
In fanfiction, Harry could faint due to some sort of magical disease or curse. There could be a new, made - up illness that affects wizards and one of its symptoms is fainting. Or perhaps he's in a situation where he's cut off from his magic for a while and his body, which is so used to having magic, goes into shock and he faints. It could also be that he's in a place with really strange or strong magical energy that his body can't handle, and this causes him to pass out.
It could be due to some kind of self - sacrifice he made in a previous battle. For example, he might have used a very dangerous spell that had a side - effect of slowly killing him to save his friends or the wizarding world.
One possible reason could be his past experiences with some cruel adults, like the Dursleys. They treated him horribly, so in fanfiction, this trauma might make him generally fearful of adults. Another reason could be his experiences with certain authority figures at Hogwarts who may have been strict or unfair, which could be exaggerated in fanfiction to create a fear of adults.
Perhaps he is betrayed by those he trusts. In the original series, there were instances of betrayal, and if in the fanfiction this is amplified, for example, if the whole wizarding community turns against him unjustly. He might feel so alone and hopeless that he loses his will to live. Also, if he discovers some dark secrets about his past that make him question his own identity and worth, it could lead to this state.
One reason could be to explore the darker side of human nature. Even though Harry is a hero in the original series, fanfiction writers might want to see how he would be affected if he was pushed to his limits. Another reason is to create a more complex and controversial storyline. It grabs readers' attention as it goes against the normal perception of Harry.
Some fanfiction writers may have a different vision for Harry Potter's character. They might see him as more of a diplomat or a healer within the wizarding world, rather than a fighter. So, they write stories that reflect this different view of the character, where he uses his wits and other skills rather than engaging in physical or magical combat.
One reason could be that the official Harry Potter canon is so extensive and detailed that it overshadows fanfiction. The original story has such a rich world, characters, and plotlines that it becomes the main focus for many fans, leaving less room for fan - created stories.