In fanfiction, Snape's own personality traits contribute to his hardness towards Hermione. He is a brooding and often moody character. Hermione's bright and positive nature might clash with his gloomy demeanor. Snape may not understand or appreciate Hermione's enthusiasm for learning in the same way other teachers do. His teaching methods are strict and unforgiving, and Hermione, with her high standards for herself, may be constantly trying to meet his expectations but always falling short in his eyes because of his unyielding nature.
Snape has a dark past and many secrets. In fanfiction, this could play into why he is hard for Hermione. His experiences with the Dark Arts and his relationship with Voldemort might make him view Hermione with suspicion. She's a Muggle - born, and in the wizarding world with its history of prejudice, Snape's own complex relationship with such issues could lead to him being hard on her. Also, Hermione's friendship with Harry Potter, who Snape has a very conflicted relationship with, could be a reason. Snape may think Hermione is involved in things that he wants to keep Harry away from, so he's difficult towards her.
One possible reason is Snape's prejudice. He might have some sort of bias against Gryffindors in general, and Hermione, being a very Gryffindor - like student, gets the brunt of it. He may expect her to make mistakes typical of Gryffindors like being overly bold without thinking. Another factor could be that Hermione is so intelligent and inquisitive that Snape feels threatened. He likes to be in control of the knowledge in his classroom, and Hermione's constant questions and thirst for knowledge might make him act tough towards her.
In fanfiction, sometimes authors like to break boundaries and explore 'what - if' scenarios. For the 'Snape cheats on Hermione' idea, it could be a way to create drama and conflict. They might be interested in exploring the emotional turmoil it would cause for Hermione, or how it could change the relationships within the wizarding world they've created in their story. It could also be a way to subvert the typical hero - heroine relationships we see in the original series.
Hermione is also very confident in her knowledge. Snape is an expert in Potions, but Hermione is no slouch either. So, when Snape tries to undermine her in Potions class, she might respond with sarcasm. For example, if Snape corrects her in a way that she thinks is wrong, she could say 'Of course, Professor, your infinite wisdom must be right' in a sarcastic tone.
One possible reason could be a misunderstanding. Maybe Hermione thought Snape was involved in some dark plot against her friends. In the wizarding world, there are often secrets and deceptions, and if she got some false information, it could lead her to take such drastic action.
One reason could be Snape's knowledge. Hermione, being a knowledge - seeker herself, might feel safe knowing that Snape has a vast understanding of magic, especially the darker aspects. So, she believes he can keep her safe from any threats related to that knowledge.
One reason could be the re - imagining of Snape's character. In fanfiction, he might be kinder and more understanding towards Hermione than in the original story. So, she feels safe in his presence.
One reason could be that Snape believes Hermione has knowledge that is dangerous if it falls into the wrong hands. So, he kidnaps her to keep her safe until he can figure out what to do with that knowledge. Another possibility is that he is being controlled by some dark magic or an outside force which compels him to take her against his will.
Some fanfiction writers might do it for shock value. They want to create a very different and extreme situation compared to the original story to attract readers' attention.
In a fanfiction, Snape might be hard on Hermione during detention. He could assign her extremely difficult tasks that are almost impossible to complete within the given time, just to test her limits. For example, making her organize his entire store of potion ingredients in a very specific and difficult - to - achieve order.
Well, Snape is a complex character. In fanfiction, he could be hard for Hermione perhaps due to their different views. Hermione is all about knowledge and fairness, while Snape has his own grudges and secrets. His past experiences, like his relationship with the Marauders and his loyalty to Dumbledore, might make him act coldly towards Hermione. He might not trust her easily, thinking she could be nosy or a threat to his plans, so he's hard on her.
Well, sometimes authors want to create a shock factor. By having Snape take advantage of Hermione, it would be a very unexpected and controversial plot twist. Also, it could be due to a lack of understanding of the characters' personalities. Snape is a proud and somewhat noble character in his own way, and Hermione is not a weakling. So this idea might come from not fully grasping their essence.