Perhaps the twins are in a more vulnerable state compared to Harry for some reason. For example, they could be sickly or have been targeted by some dark wizards from the start. So, the Potters, in their attempt to protect the more 'at - risk' children, end up neglecting Harry.
It could also be that the Potters are under some sort of magical influence or curse. In the fan fiction world, there could be a dark force at play that makes them see the twins as more important. This force might be manipulating their emotions and perception, leading to the neglect of Harry.
One possible reason could be that the twins might have some special abilities or circumstances that draw the Potters' attention more. Maybe they are more outgoing and seem to need more immediate care or guidance. Another reason could be that there is some sort of miscommunication or misunderstanding within the family. For example, the Potters might think Harry is more self - sufficient when in fact he also needs their love and attention.
Harry might become withdrawn and introverted. Feeling unloved and unwanted, he could start to keep to himself more, spending time alone in his room or exploring the grounds of their home alone, trying to make sense of why his parents seem to favor the twins.
He might become withdrawn. Feeling unloved and ignored, Harry could start to keep to himself more, not sharing his thoughts and feelings with his family. He may also become resentful towards the twins, seeing them as the cause of his being neglected, even if it's not entirely their fault.
Perhaps there's a plot against Harry by some dark forces, and the Potters believe that only they can protect him properly. They might think that the people who have been taking care of Harry so far are not equipped to handle the new and more dangerous threats. Also, it could be that the afterlife in the wizarding world has some rules or opportunities that allow them to try and get Harry back into their family fold. They could have been given a second chance, so to speak, and are eager to take it.
I'm not sure specifically if there is a 'Potter's Neglect Harry' gay fan fiction. Fan fiction is a vast and diverse realm, and while there are many types of Harry Potter fan fictions, this particular one may or may not exist. It could depend on the creativity and interests of individual fan fiction writers.
One possible motive could be that the Potters discovered some dark plot by the Malfoys involving Harry. Maybe they found out that the Malfoys were planning to indoctrinate Harry into their pure - blood supremacist ideology against his will. So, to protect Harry from that, they kidnapped him.
Another possibility is that Harry could find a hidden diary of his parents. The diary could contain their thoughts, experiences at Hogwarts, and even some secrets about the wizarding world that they were involved in. It would give Harry a more personal connection to his parents and their lives before him.
Sirius Black could also be part of it. He was Harry's godfather. He might have escaped from Azkaban earlier in this fanfic. He teams up with the Potters to rescue Harry. He could be the one who scouts out the Dursleys' house before the actual rescue operation, using his skills as an Animagus to stay hidden.
Well, in this fan fiction, it might be that Hermione moves in with the Potters due to some post - war reconstruction efforts. She could be helping to restore Hogwarts or the wizarding community in general, and living with the Potters gives her a stable base. Also, it could lead to some interesting family dynamics, like Hermione teaching the Potter kids all the things she learned at Hogwarts, and creating new spells and potions together.
Sally could be in a new relationship or have new friends that are demanding a lot of her time. As a result, she may not have as much time or energy to devote to Percy, which unfortunately comes across as neglect in the fanfiction.