They are popular because it shows Hermione in a vulnerable state. Usually, she's so strong and in control, but when she's sick, it's a new side of her.
There's a fanfic titled 'When Hermione Falls Ill'. In this story, it focuses on Hermione's internal struggle while being sick. She's not used to being incapacitated and it delves into her thoughts and how she copes. It's really interesting as it gives a deep look into her character even when she's not at her best. For example, she tries to continue her studies while sick but her body just won't allow it.
In this fanfic, Cleo getting sick could lead to some interesting plot developments. Maybe it shows how the other characters in H20 react to her being ill. They might have to take care of her, which could strengthen their relationships.
Her best friend Veronica would probably be one of the first to help. Veronica is wealthy and could use her resources to get the best doctors for Betty.
Obviously, her best friends Sam and Freddie would visit her. They are always there for each other. Maybe Gibby would also come over with his unique brand of humor to try and cheer Carly up.
Another theme is the vulnerability of a strong character. Hermione is usually very intelligent and in control, but when sick, she becomes vulnerable. This allows for character development as she has to rely on others, and we see a different side of her. In many fics, she might have to accept help from unexpected characters.
I'm not entirely sure specifically as it could be a very niche or even a made - up fanfic title. It might be a fan - created story related to some sort of 'selection' process in an 'America gets sick' scenario. Maybe it's about a selection of people to deal with a disease outbreak in America in a fictional and creative way.
One common theme is friendship. When Ash gets sick, his friends usually rally around him. For example, Pikachu might stay by his side constantly, and his human friends like Misty and Brock would try to find remedies or take care of him. Another theme could be vulnerability. Ash is often seen as a strong and determined trainer, but when he's sick, it shows his more vulnerable side.
The following are a few recommendations for novels where the male lead gets jealous and falls ill: " Forced Subjugation ": The male protagonist displayed extreme possessiveness and jealousy. He even hid the protagonist and did not allow anyone to meet him. 2. " Medical Beauty: The Evil Concubine of the Sick and Delicate Prince ": The male protagonist is paranoid and has a strong jealousy plot towards the female protagonist. These novels all had plots where the male lead was jealous and fell ill, so they were suitable for readers who liked this type.
Another possibility is that one of the other characters in PLL has a hidden motive. For instance, someone who is jealous of Allison's popularity or someone who she had an argument with in the past. They might have found a way to make her sick without being suspected at first.