The popularity lies in the fact that it combines two well - loved characters, Harry and Draco, with a fascinating magical element like the werewolf curse. It gives fanfiction writers a lot of room to play with different storylines. They can explore how the transformation affects Draco's family relations, Harry's role as a friend or protector, and how the entire Hogwarts community reacts. It also creates opportunities for romantic or platonic relationship development between the two in a very unique context.
These fanfictions are popular because they allow for exploration of themes like acceptance and prejudice. In the wizarding world of Harry Potter, werewolves are often discriminated against. When Draco or Harry are involved in the werewolf scenario, it gives a chance to show how they deal with the prejudice, either as the victim (if turned into a werewolf) or as an ally. It also adds a layer of mystery and danger to their relationship, which is appealing to readers.