Perhaps he simply lost his creative inspiration. Fanfiction writing often requires a constant flow of new ideas, and if he's been through a lot of stress or has had some personal issues, like his complex relationship with Lily still haunting him, it could dry up his well of creativity.
It could also be due to some external factors. Maybe there are threats from dark forces that he doesn't want to involve Lily in. If he is getting deeper into the dark arts or some dangerous situations, he might choose to give up on her to protect her from the potential harm that could come her way because of his associations.
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.
Maybe Stiles has been constantly disappointed by Derek's actions or lack of response in the fanfiction. It could be that Derek has repeatedly let Stiles down, and over time, Stiles just can't take it anymore.
One reason could be repeated heartbreaks. If she has been through multiple bad relationships with men in the fanfiction, it would lead her to give up. Maybe she constantly faced betrayal or being taken for granted.
One possible reason could be that he realizes his feelings are unrequited. In the fanfiction, perhaps Lily has made it clear she doesn't have the same feelings for James, so he gives up. Another reason might be external factors. For example, there could be some sort of danger or situation that makes James think he needs to step back from Lily for her own good.
One possible reason could be that Sakura realizes Sasuke is too consumed by his revenge and she can't keep waiting for him to change. She might see that he is constantly putting her in a secondary position and she decides she deserves better. For example, Sasuke has left the village multiple times, leaving Sakura heartbroken each time.
One reason could be the constant setbacks he faces. He might feel that no matter how hard he tries, he can't achieve his goal. For example, if he fails too many times in battles against strong opponents, he could lose hope. Another reason might be the loss of important people in his life. If someone like Iruka or Kakashi, who have been his pillars of support, were to die, it could shatter his dreams as they are so closely tied to his will to succeed for their sake.
One possible reason could be Snape's unfair treatment of Gryffindor students. Hermione, being a strong advocate for justice, might not tolerate his constant jabs at her house. For example, in the original story, Snape often took points from Gryffindor without what Hermione might consider proper cause. In fanfiction, this could be exaggerated, leading to her blowing up at him.
One possible reason could be that Snape is secretly trying to protect Harry. Maybe the potion has some sort of protective charm or antidote against a dark magic threat that Snape has foreseen. He may not show it openly, but his actions are driven by his long - standing, complex feelings towards Harry's mother and his sense of duty.
It might be that Ash has other priorities now. For example, real - life commitments such as work or study have taken up too much time, leaving no room for writing fanfic.