Static characters don't really change throughout the story. That's why they need to have multiple sides to them, so they can be compelling. They can also inspire change in others.
The victim of the revenge fic would just mindlessly suffer because of plot. Why doesn't anyone in-universe do anything about it? Because the story actively restrains them from doing anything. The victim would be Unintentionally Sympathetic, Goanimate Punishment Day style.
Static characters don't really change throughout the story. That's why they need to have multiple sides to them, so they can be compelling. They can also inspire change in others.