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.
Sakura might grow tired of Sasuke's cold and distant behavior. In fanfiction, she could realize that she's been trying too hard to hold on to a relationship where she's not getting the love and attention she deserves. Maybe she meets someone else who shows her more care and respect, which makes her consider breaking up with Sasuke.
On a larger scale, it might change the way the story views the concept of unrequited love. Instead of the typical 'waiting for the loved one' trope, it shows that characters can move on. This can be an important message for readers, especially those who can relate to being in a one - sided love situation. It also might shift the focus of the story more towards Sakura's personal growth and her new goals, rather than the Sasuke - centered plot that it might have been before.
Maybe Naruto gets tired of always chasing after Sasuke. He has his own life and dreams too. He might think that he has sacrificed enough of his time and energy on Sasuke, and it's time to focus on himself and the village. He could start to believe that Sasuke has made his own choices and he can't keep forcing Sasuke to come back.
One possible storyline could be that Sakura realizes Sasuke is too consumed by his revenge and she decides to focus on herself. She might start training harder to become a better ninja in her own right, perhaps specializing in medical ninjutsu even more. This could lead to her making new friends and allies within the village, and she could end up being a key figure in Konoha's development, without Sasuke in the picture.
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.
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.
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.
In some fanfictions, Sasuke could be under the influence of some dark power or curse. This power might compel him to kidnap Sakura. For example, a dark entity might want to use Sakura's abilities or her connection to Sasuke for its own evil purposes, and Sasuke, being unable to fully control himself, follows its commands.
One possible reason could be Sasuke's pursuit of power. In many fanfictions, his thirst for greater strength might lead him to leave Sakura behind as he embarks on a solo journey to train in more dangerous and secluded places. He may feel that his goals are too dangerous for her to be involved with.
One possible reason could be a lack of communication. If Sasuke is always away on his missions and doesn't share his thoughts and feelings with Sakura, it can create a rift. Another reason might be differences in their long - term goals. For example, Sakura may want a more stable family life, while Sasuke is still too focused on his pursuit of power or justice in the shinobi world.