It could be that in this fanfiction, Ash had some personal issues come up. For example, he might have received some bad news from his family back home that made him lose focus on training and eventually give it up. Another reason could be that he found a new passion or interest that diverted his attention away from training.
In the 'Ash gives up training fanfiction', one possible reason is that he felt like he wasn't making any progress despite his best efforts. He might have been training for a long time without seeing any significant improvement in his skills or abilities. This lack of progress could have led to frustration and ultimately, his decision to give up training. Also, he could have been influenced by other characters in the fanfiction who convinced him that training wasn't the right path for him.
One possible reason could be a lack of time. Maybe Ash has become too busy with other aspects of life, like work or studies, and can't find the time to write fanfiction anymore.
Maybe the loss of a very dear Pokémon friend. If something bad happened to a Pokémon he was extremely close to, like it getting seriously injured or lost forever, it could be so devastating that he loses the will to continue his journey and thus gives up.
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.
It could also be that he is tired of the false expectations created by fanfiction. In fanfiction, his character might be portrayed in ways that don't match who he really is. He wants to be true to himself and his ninja way, so he gives up fanfiction.
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.
Well, he might start exploring other aspects of the Pokémon world, like studying Pokémon behavior or focusing on Pokémon care.
One possible reason could be that she loses inspiration. Maybe she has explored all the ideas she initially had for her fanfiction and can't come up with new and exciting storylines. Another reason might be lack of time. If she gets involved in more important or urgent matters in the RWBY universe, she simply doesn't have the hours to sit down and write fanfiction anymore. Also, she could face criticism from others which makes her lose confidence in her writing and decide to give it up.
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.
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.