Maybe it's because he admires her intelligence. Hermione is known for her vast knowledge of magic, and Charlie, who has his own area of expertise with dragons, might respect that. He sees her as someone worth protecting because she could contribute a great deal to the wizarding world, and he doesn't want to see that potential lost.
Moony might be protective of Hermione because he has a strong sense of justice. In the wizarding world, Hermione is a Muggle - born, and she often faces discrimination. Moony, being a member of the Order of the Phoenix, is against all forms of prejudice. He would naturally want to protect her from any harm, whether it's from Death Eaters or just general bigotry within the wizarding community. Also, Hermione's intelligence and her role in fighting against the dark forces make her an important asset, and Moony would understand the need to safeguard such a valuable ally.
One reason could be that they see her intelligence as an asset. Hermione is known for her brilliant mind, and Slytherins, who value cunning and resourcefulness, might respect that. They could also recognize her strength in the face of adversity and be drawn to protect her as a way to show their own growth beyond the typical Slytherin - Gryffindor rivalry. In some fanfictions, a Slytherin might have a personal connection or debt to Hermione, which leads to their protective nature towards her.
In many fanfictions, Remus might be protective of Hermione because he sees her great potential and intelligence. He could also feel a sense of duty as an older, more experienced wizard. Additionally, he may have witnessed some of the hardships she has faced at Hogwarts and wants to shield her from further harm.
In fanfiction, Harry might be protective of Hermione because of their deep friendship. They've been through so many dangerous adventures together in the original series. Harry values Hermione's intelligence and loyalty, and he doesn't want to see her get hurt. It could also be that in some fanfiction, there are new threats or situations that make him feel the need to be extra protective.
In fanfiction, it might be due to a redemption arc for Lucius. He realizes the error of his ways in the wizarding war and starts to view Hermione, a muggle - born with great talent, as someone worthy of protection. He could also be protecting her from other dark wizards who might want to harm her because of her intelligence and influence among the light - sided wizards. This protection could also be a form of self - atonement for his past misdeeds against the muggle - borns.
One reason could be that he sees her intelligence and potential. Snape has always had a soft spot for those who are brilliant in potions and magic, and Hermione is top - notch in that regard. He might also recognize her determination and how she's often an outcast among her peers in a way, just like he was. So, he feels a sense of kinship and thus protectiveness towards her.
In the wizarding world, there are always threats lurking. Hermione, with her inquisitive nature, sometimes gets into situations where she might be in over her head. Sirius, having a wealth of magical knowledge and experience, is seen as a perfect character to be her protector. Fanfiction writers like to play with this idea, showing how he can use his skills and instincts to keep Hermione out of trouble and safe from harm. It also adds an interesting layer to the relationships within the Harry Potter universe.
One example could be in a story where Hermione is in danger during a wizarding battle. Charlie, being protective, might swoop in on his dragon and shield her from the incoming spells. He could then take her to a safe location, away from the chaos of the battle, while constantly keeping an eye out for any potential threats.
It's popular because it offers a different perspective on their relationship. In the original series, they are sort of enemies. But in fanfiction, seeing Draco be protective of Hermione gives a sense of novelty. People like to explore the idea of characters changing and growing in unexpected ways.
Authors write this trope because it creates an interesting dynamic. Draco, coming from a Slytherin background and often being seen as a rival to Hermione's Gryffindor values, suddenly being protective adds a new layer of complexity to their relationship. It's a form of 'enemies - to - lovers' or at least 'enemies - to - allies' which is very appealing to readers.