What are the possible reasons for a 'Harry is abused by Lily' fanfiction?

It could be an exploration of the darker side of human nature. Writers may use these characters to show how relationships can go horribly wrong, even if it's not in line with the original story.

In some fanfics, it could be due to a threat she believes she can't protect Harry from. Maybe she thinks that by leaving him, the dark forces won't target him as much.

One reason could be for shock value. Some authors like to create extreme and unexpected scenarios to get a reaction from readers. Another could be a different interpretation of Harry's character. Maybe they see some latent flaws in him that could lead to such behavior in certain extreme situations.

Perhaps in this fanfic, Harry has been influenced by dark magic or some evil entity. This external influence could distort his perception of Lily and turn his normal feelings for her into hatred. Dark magic has the power to corrupt one's mind and change relationships in unexpected ways.

Perhaps they are blackmailed. A powerful dark wizard could threaten to harm all of their friends and family if they don't abandon Harry. They may feel they have no choice but to sacrifice their relationship with their son to protect others they care about.

Well, it might be because some fans feel that Slytherin has been somewhat demonized in the original books. So, they create fanfiction where Slytherin is the victim of abuse, perhaps as a way to give the house more depth and sympathy. Also, the idea of abuse can create a lot of drama and conflict, which are elements that make a story interesting. Fanfiction writers might be using this concept to attract readers who are interested in more complex and edgy storylines. Additionally, it could be a form of exploring the morality and ethics within the Harry Potter universe in a very extreme way.

Some people might create this kind of fanfiction out of a desire for a very different and edgy take on the characters. They want to explore the darker side of relationships, even if it's completely against the original portrayal of Ron and Harry's friendship.

Well, some writers might do it to explore the idea of nature vs. nurture. If Harry was Voldemort's son, how would his upbringing with the Dursleys and his experiences at Hogwarts shape him differently? It could also be a way to rewrite the entire story arc in a more subversive way. Maybe the writer wants to see how the wizarding world would react to such a revelation. And of course, for some, it's just a way to be creative and break all the rules of the original story.

One reason could be jealousy. Maybe Snape gets jealous of Lily's other relationships or her popularity at Hogwarts. Another could be a fundamental difference in their beliefs or values that grows over time into hatred.

It could be that in fanfiction, Snape has been through some additional trauma or experiences that change his perception of Lily. For instance, if he discovers something about Lily that he doesn't like, such as her involvement in some secret or her having a different side to her character that he finds unappealing. This would cause him to dislike her, as opposed to his more nuanced feelings in the original story.