It could also be that Harry is constantly being ostracized and misunderstood by the wizarding world he has been trying to protect. Despite all his good deeds, if people start to turn against him, accusing him of things he didn't do. He might just feel so alone and betrayed that he loses his motivation to live and decides to give up on life.
Maybe in the fanfiction, Harry discovers some dark secrets about his past that make him question his whole existence and purpose. Like if he finds out that his parents' sacrifice was part of some bigger, more sinister plan, he could become so disillusioned that he gives up on life. He might think that everything he has been through was a lie and there's no point in going on.
It could be that Naruto has a vision of a different kind of life or place where he can truly be at peace. He might meet someone from another village or group who shows him an alternative way of living that is more appealing than staying in Konoha. And so, he gives up on Konoha to pursue this new path.
Perhaps Dumbledore is being forced in this fanfiction. There could be some dark magic or powerful dark wizard threatening Hogwarts or the wizarding world. Dumbledore, in a desperate attempt to save everyone else, gives Harry to Voldemort as a sacrifice. But Harry, being the hero he is, could find a way to turn the situation around and defeat Voldemort from within his lair.
One possible reason could be that J.K. Rowling, the author of Harry Potter, has strict control over the franchise and might have made some regulations that made it difficult for him to continue. Another reason could be that he simply lost interest in writing fanfiction about it. Maybe he wanted to focus on creating his own original stories instead.
One possible reason could be that Ginny realizes Harry is too preoccupied with his heroic duties and she feels neglected. In fanfiction, this is a common trope where the female character desires more attention in a relationship.
Hermione could be a main character. She might be the one trying to pull Harry out of his despair. Or she could be in a similar state herself, having witnessed Harry's downward spiral, which adds to the overall gloom of the story.
The story could be that Harry grows up alone in the Muggle world, completely unaware of his wizarding heritage until much later. He might face bullying and isolation in the Muggle school. When he discovers his true identity, he has to quickly adapt to the wizarding world all by himself. This could lead to him making some hasty and unwise decisions as he has no one to guide him.
Perhaps in the 'harry gives birth at dursleys fanfiction', there's a new form of magic introduced. Harry could have been affected by a magical experiment that causes this strange phenomenon. The Dursleys, who have always mistreated Harry, now have to face the consequences of having such a unique and unheard - of event happening in their house. They might be in a state of panic and confusion as they try to figure out what to do.
The plot could be that Harry, perhaps from the wizarding world, is invited to give a guest lecture at a magical school. He might share his adventures, like the battle against Voldemort, and inspire the students with his tales of courage and friendship.
Perhaps the 'bro' is a place that has some special properties. Harry enters this 'bro' place, and due to the energy or magic there, he undergoes a transformation that leads to giving birth. The story could then be about Harry coming to terms with this new situation, dealing with the physical and emotional changes, and trying to find out how to reverse it or at least live with it.
It could be about a moment of unexpected passion between Harry and Draco. Maybe they have a secret relationship and in a moment of intimacy, Harry gives Draco a hickey. This could cause all sorts of drama in the wizarding world as they try to keep it a secret from their friends and enemies alike.