Why are dead parents a common trope in fiction?

One reason could be the contrast between their characters. Draco is from a pure - blood family with a sense of entitlement, and Hermione is a Muggle - born witch. His possessiveness can add an element of drama. It might also be because in the original series, there was always an underlying tension between them, and fanfiction writers explore this further in a romantic or obsessive - possessive context.

In the Naruto universe, Naruto is a powerful character. Hinata, while strong in her own right, is not as physically dominant as Naruto in many fan interpretations. Naruto's overprotectiveness can show his growth as a character who now has someone he cares deeply about. It also creates drama and tension. For example, when they face enemies together, Naruto's overprotective nature can lead to him making rash decisions or Hinata trying to prove herself despite his protection, which makes for an interesting plot in fanfiction.

One reason could be that it plays on primal fears. Also, it can be used to symbolize the vulnerability of humans in the face of powerful, malevolent forces.

No. Usually, more common tropes in science fiction are about robots, space exploration, or time travel. Tree Boy is a rather unique concept not often seen.

It's not an extremely common trope in the mainstream Harry Potter fanfiction world. However, some writers might explore this idea for the sake of novelty or to subvert traditional gender roles. In the original series, Harry is male, so this concept goes against the norm. But in fanfiction, it allows for creative exploration of different scenarios, like how the wizarding world would react to such an unexpected situation, and how Harry himself would deal with the physical and emotional changes.

No. They are not that common. Most science fiction focuses on more traditional types of mutants like those from scientific experiments gone wrong in urban or futuristic settings. The 'hillbilly' aspect combined with the mutant and genius elements is a rather unique and less explored concept.

A trope in fiction is a recurring concept or motif. Like the 'love triangle' or the 'hero's journey'. They give a kind of predictability and structure to stories, but can also be used in creative ways to surprise and engage the audience.

One common trope is the 'hurt/comfort' where a character gets injured or is in emotional pain and another character helps them heal.

No. It's not a common trope as such relationships are often considered unethical and inappropriate. Most literature focuses on healthy, consensual relationships. However, in some works that explore complex social and moral issues, it might be touched upon briefly to highlight problems like power imbalances.

Well, in the Potterverse, Snape is a very polarizing character. Some fans love him, and some don't. Those who don't might be more likely to write him as a bully in fanfiction. It could also be that they want to create an 'underdog' situation for Harry. By having Snape bully him, Harry becomes more of a hero when he stands up to it or finds a way to deal with it gracefully.