Another possibility is that some sort of magic or other - worldly force has made him disappear. In fanfiction, there are often all kinds of wild ideas. For example, a powerful sorcerer might have accidentally sent him to another dimension while trying to protect him from an enemy.
It could also be related to his identity being discovered in a really bad way. He might have decided to disappear to protect his loved ones from the potential danger that comes with being associated with Spider - Man. So he just vanishes to start a new life where no one can find him.
Well, one reason could be that he's on a secret mission for S.H.I.E.L.D. that requires him to go undercover and cut off all contact. Maybe he's investigating a new super - villain threat that's too dangerous to let anyone know about.
Maybe it's due to a new and powerful enemy's attack. In fanfiction, authors might create unique villains with abilities that specifically target Peter's weaknesses. For example, if the villain has the power to disrupt Spider - Man's enhanced senses, it could cause Peter to be disoriented and ultimately collapse. Another aspect could be that Peter overuses his powers without proper rest, which exhausts his body and causes him to collapse.
One possible reason could be extreme exhaustion. Peter Parker has a double life as a student and Spider - Man. He might be overworked, not getting enough sleep, and his body just gives out. For example, he could have been fighting multiple villains in a row without a break.
He might think it's not in line with the real Steve. Fanfiction can be quite far - fetched sometimes.
Well, it might be an exploration of the psychological toll of being a superhero. Peter Parker constantly faces danger, loss, and has to keep his identity a secret. Writers may create 'suicidal peter parker fanfiction' to show how all these factors could potentially break him. Also, in the context of fanfiction, it could be a way to subvert the typical heroic narrative and show a more vulnerable and broken side of the character. However, it's a very heavy and potentially triggering topic.
One reason could be that Peter realizes he still has unresolved feelings for Gwen from his past. Maybe something happens that makes him remember their relationship more vividly.
One possible reason could be a difference in ideology. Maybe Peter Parker feels that Stark's methods are too extreme or not in line with his own moral compass. For example, Stark might be involved in some projects that Peter doesn't agree with, such as using certain unethical technologies in the pursuit of justice.
One possible reason could be that Peter is keeping secrets from MJ about his Spider - Man identity. In many versions, his secrecy creates misunderstandings and MJ might feel left out or betrayed, leading to her crying.
Some writers might do it for shock value. They want to create a very different and extreme take on the character to get a strong reaction from readers.
One reason could be extreme guilt. Maybe he failed to save someone important and can't bear the burden of that failure. In some fanfictions, if he accidentally caused harm to his loved ones, like Aunt May getting hurt because of his superhero activities, the guilt might be overwhelming.
It could also be a way to subvert the typical superhero narrative. Usually, superheroes are invincible and always triumph. By writing about Peter Parker committing suicide, it challenges the norm and makes readers think about the fragility of even the most iconic characters. It forces the audience to consider the toll that being a hero can take on a person's mental and emotional state.