His obsession with power and revenge is another factor. If in fanfiction he continues to pursue his dark path without considering how it affects Sakura, she would surely be angry. Imagine he gets involved in dangerous battles without a thought for her worry.
Well, Sasuke's cold attitude could be a reason. He is often distant and unresponsive to Sakura's feelings in the original story, and in fanfiction, this can be exaggerated, making Sakura angry. For instance, if he ignores her attempts at conversation or help.
One possible reason could be Sasuke's continued obsession with his revenge - even after they got married, his focus on past grudges might have driven a wedge between them. Another could be differences in their life goals. Sakura might have wanted a more settled family life, while Sasuke was still drawn to his wandering ways in the name of protecting the village from afar.
Well, one possible reason could be that Sasuke's mistake might have put their team in great danger. For example, if his actions led to the enemy getting an upper hand during a battle, endangering not only his life but also those of his comrades like Sakura. Sakura, who values the safety of the team, would then resent Sasuke for his mistake.
Protectiveness. Sasuke has seen a lot of danger in his life. He knows Sakura is a valuable person, both as a friend and as someone he cares about. So his possessiveness could stem from his desire to keep her out of harm's way. He doesn't want any bad guys to get near her.
One reason could be a misunderstanding. The fanfic might have set up a situation where Sakura misinterprets Itachi's actions. For instance, she could think he is plotting against her when in fact he has good intentions.
One possible reason could be that Sasuke is too focused on his revenge. His single - minded pursuit of power and vengeance against Itachi leaves little room for romantic feelings. He might see a relationship with Sakura as a distraction from his goals.
One reason could be that in some fanfiction, the characterizations of Sasuke and Sakura might be off. Maybe Sasuke is portrayed as overly cruel to Sakura in a way that doesn't seem true to his character in the original series. Another reason could be that the storylines in these fanfictions are too clichéd, like always having Sasuke constantly reject Sakura in the same uninteresting ways.
In fanfiction, Sasuke might snap at Sakura due to miscommunication. Sakura could be expressing her concern for him in a way that he misinterprets. For instance, if she tells him not to go on a dangerous mission and he thinks she is trying to control him instead of just caring about his safety. Another factor could be the influence of external forces. Maybe there are other characters or events that put him in a bad mood, and Sakura just happens to be there at the wrong time, so he snaps at her.
It could also be a way for the writer to express their own dissatisfaction with the original relationship between Sakura and Sasuke. Maybe they felt that Sakura's character was not well - developed in the context of that relationship and decided to create a more 'dramatic' storyline through cheating.
One reason could be to create drama. The idea of a relationship being broken by cheating is full of emotional turmoil which can make for an interesting read. Another reason might be some writers' preference for the Sasuke - Karin dynamic. They might see potential in their relationship that wasn't explored in the original series.
Sakura might cry over Sasuke because of the distance between them. In many fanfictions, Sasuke goes off on his own journey, leaving Sakura behind. She misses him and the pain of separation makes her cry. Additionally, if Sasuke gets injured severely in a fight, Sakura, being a medic, might cry out of worry for his well - being and the possibility of losing him.