One possible reason could be that he might feel abandoned. Growing up without them, he could resent the fact that they left him an orphan. He might think that if they were really so great, they would have found a way to survive and be there for him.
One possible reason could be that in the fanfic, the author might twist the story to make it seem like his parents' actions had unforeseen consequences that affected Harry negatively. For example, their fight against Voldemort led to Harry being an orphan and having to bear a great burden from a young age.
One possible reason could be some past misdeeds by the parents. Maybe they were neglectful or made decisions that seriously affected Ciel's life in a negative way in the context of the fanfic.
The original Harry Potter story has a strong family - love - centered theme. Harry's parents' love for him was so strong that it protected him even after their death. In the 'Harry Potter hates his parents' fanfic, this central theme is completely changed. It's a deviation that changes the whole dynamic of the relationships in the story. It's like changing the core of a flower, everything else about the story will be affected, such as Harry's relationship with his friends who also respected his parents.
On a more magical level, reviving the dead is against the natural order of things in the wizarding world. This could attract unwanted attention from magical authorities or even dark forces. Some might see Harry's act as a dangerous precedent and try to either stop him or use his new - found power for their own evil purposes.
In some fanfictions, Harry might use extremely powerful and ancient magic. Maybe he discovers a long - lost spell during his adventures that has the power to reverse death. For example, he could find a spell hidden in a forgotten corner of the Hogwarts library that was created by a powerful wizard in the past but was deemed too dangerous to be used.
The portraits could offer him emotional support. Just seeing his parents' faces might give Harry the strength to face difficulties. For example, when he's feeling down or facing a tough decision, looking at the portraits could be like getting a warm hug from his parents, even if they're not physically there.
In fanfiction, Harry crying for his parents is a very emotional and powerful moment. It often shows his deep longing and pain for the family he lost. Writers may use this to explore his character's vulnerability and the lasting impact of his parents' death on him.
Yes, there might be some extremely dark and out - of - canon fanfictions out there with such a disturbing premise, but it goes against the general nature of the original story where Harry's parents loved him deeply. However, in the vast world of fanfiction, people can create all kinds of strange and often inappropriate scenarios.
The original story builds Harry as a hero who honors his parents' legacy. In the 'harry potter hates his parents fanfiction', his development takes a different path. He may not strive to be the hero that his parents would have wanted him to be. Instead, he could be on a journey to break away from their shadow, which is the opposite of the growth we see in the original story where he embraces his heritage and uses it as a strength.