It could be for the greater good of the village. There might be a prophecy or some sort of political situation where Sakura's pretend love for Naruto is seen as a way to strengthen the village. For example, their union (even if it's fake) could be a symbol of unity that would boost the morale of the villagers and make other villages see them as more stable and powerful. Also, Sakura might be pressured by the elders or some authority figures in the village to do this in order to maintain a certain image or alliance.
Well, in the fanfiction context, Naruto may not love Sakura because he has unrequited feelings for someone else. Maybe he has a deep connection with another character that makes him view Sakura just as a teammate. Also, their personalities might not be as compatible in a romantic sense as one would initially think. Naruto is often impulsive and headstrong, while Sakura can be a bit more reserved in some ways, and this could lead to a lack of romantic attraction.
Maybe she wants to experience the story from a male perspective. In fanfiction, different genders often have different roles and experiences. By pretending to be male, Sakura can explore how male characters are written, how they interact with others, and what kind of emotions and challenges they face.
One possible reason could be that she might have underestimated Naruto in the past. She often belittled his abilities and dreams, but as she grew and realized his true strength and determination, she felt the need to apologize for her previous behavior.
One reason could be to protect his friends. Naruto doesn't want his friends to worry about him, so he pretends to be happy even when he's facing difficulties. For example, when dealing with the threats from powerful enemies, he shows a happy face to keep his team's morale up.
Perhaps Sakura is in a state of extreme stress. Maybe she has a lot of pressure on her, like trying to save a village or a loved one, and Naruto's actions, which might seem reckless to her at the time, cause her to snap and hurt him without really meaning to.
One possible reason could be Sakura's constant pining for Sasuke. Naruto might feel frustrated that she's so focused on Sasuke when he's right there for her. In the Naruto universe, Naruto has always been a bit jealous of Sakura's love for Sasuke, and in fanfiction, this could be amplified to the point where he yells at her out of pent - up emotions.
One reason could be Naruto's recklessness. In fanfiction, Naruto might do something extremely dangerous without thinking, and Sakura, being worried about his safety, yells at him. For example, if he decides to take on a powerful enemy alone without a proper plan.
Maybe Naruto is sick of Sakura in fanfiction because her character is often portrayed as too pushy or one - dimensional. In some fanfictions, Sakura might be overly obsessed with Sasuke and Naruto just gets tired of her constantly going on about it.
One reason could be miscommunication. Maybe Sakura said something that Naruto misinterpreted as an insult to his dreams or abilities. For example, if she made a comment about his progress as a ninja in a way that came off as dismissive.
One reason could be that Naruto realizes his feelings for someone else and doesn't want to mislead Sakura. In some fanfictions, Naruto might discover that his true love is Hinata and so he steps away from Sakura to pursue a relationship with Hinata without causing any confusion for Sakura.