It could also be because of relationship incompatibility. Hermione is highly intelligent and driven, and Severus is a complex and often brooding character. Their different personalities might clash in the fanfiction. For instance, Hermione might feel that Severus doesn't support her academic or social pursuits enough, or Severus might find Hermione too outspoken and interfering in his solitary world.
One possible reason could be that the fanfiction deviated too much from the original character traits of Hermione. Fanfiction often takes creative liberties, and if it strays far from what makes Hermione who she is in the original series, it might make her seem out of character, leading to a decision to leave.
One reason it could be popular is the allure of the forbidden or unexpected. Ron and Hermione were a well - known couple in the original series, so the idea of Hermione leaving him for Severus is a huge deviation. It also gives a chance to delve deeper into Severus' character. Fans might be interested in seeing how he would react to such a relationship.
One reason could be that the writer wants to explore new storylines without his character. Maybe they feel his arc has reached a natural conclusion in their fanfic universe. For example, if the story has been centered around Tim Drake's detective work for a long time, the writer might decide to shift the focus to other characters by having him leave.
One possible reason could be a misunderstanding. Maybe there was a miscommunication between them, like Ginny thought Harry was still too preoccupied with his past traumas and not fully committed to their relationship. Another reason might be external pressure. In some fanfictions, there could be outside forces, such as dark wizards threatening Ginny and she leaves Harry to protect him.
One possible reason could be that he feels he's a liability to the pack. Maybe he doesn't have the same supernatural abilities as the others and fears he'll hold them back during dangerous situations.
Hermione might see Severus as a very intelligent and powerful wizard. She could be attracted to his knowledge of the Dark Arts and Potions, and think that their child would inherit great magical abilities. Also, Hermione might believe that she could redeem Severus through their relationship and having a child together would be a symbol of that new start.
One possible reason could be the contrast between their characters. Lucius is from a traditional pure - blood family, while Hermione is a Muggle - born witch with great intelligence. The idea of these two very different characters interacting in fan - created scenarios might be fascinating to him.
Perhaps it's about the idea of corruption. Bellatrix, being on the dark side, might be obsessed with Hermione as a symbol of the light side that she wants to taint. In fanfiction, it could be a way to show the struggle between good and evil in a more personal and complex way. Also, Hermione's courage in the face of danger might be something that attracts Bellatrix's attention in these fictional stories.
Well, in fanfiction, anything can happen. Hermione leaving Ron for Severus might be a way for writers to show Severus in a different light. Perhaps they see Severus as someone who has been misunderstood and Hermione, being the intelligent and perceptive character she is, could be the one to recognize his true worth. But it also shakes up the core relationships we knew from the original series, which can make some fans uncomfortable.
One reason could be that he discovers a new threat and decides he can't stay with the Dursleys any longer for their safety. Another might be that he simply can't bear their mistreatment anymore and finds an opportunity to escape.