Perhaps in this fanfiction, there's a prophecy that is misinterpreted. The prophecy might seem to suggest that Harry will bring great danger to England in the future. So, the magical authorities decide to kick him out as a precautionary measure. It could also be related to some ancient magic laws that Harry has unknowingly violated, which leads to his expulsion from England.
One possible reason could be that in the fanfiction, the wizarding community in England has turned against Harry due to some false accusations. Maybe a powerful dark wizard has framed him for a series of heinous crimes, and the public, being misled, forces him to leave. Another reason might be political intrigue within the Ministry of Magic. There could be a new regime that sees Harry as a threat to their power and thus kicks him out.
It could be that Harry has made some powerful enemies in the fanfiction who have managed to influence the entire wizarding society against him. They spread rumors and lies about him, causing the general public to lose faith in him. Additionally, if there are some new and extreme magical purity laws in the fanfiction, Harry, being a half - blood, might be targeted and kicked out.
Harry might be initially shocked and angry. He has always considered England his home and fought for it. So, being kicked out would be a huge blow. He may try to fight back, using his magic to resist the unjust decision. However, if he realizes that resistance is futile, he could leave with a sense of bitterness and a determination to one day clear his name.
One possible reason could be miscommunication. Maybe Harry does something that Sirius misinterprets as a betrayal or a stupid mistake, leading to Sirius lashing out.
One reason could be that he's tired of the constant danger and politics in the magical world. He might want a normal life away from all the dark wizards and power struggles.
Maybe he's tired of the spotlight in England. In some fanfictions, he could be seeking a new start away from the prying eyes and the constant media attention that comes with being in England.
Well, perhaps Harry Potter has grown frustrated with the Order's methods. Maybe he feels that they are too cautious or not taking enough risks in the fight against Voldemort. So, he decides to break away and form his own group with a more aggressive approach to dealing with the dark forces.
Well, it could be that Harry, at that moment, saw Draco not as his rival but as a fellow student. In the wizarding world, Quidditch can be a very dangerous sport. Harry might have thought about how his friends would feel if he were in Draco's position. Also, Harry has a heroic streak. He might have instinctively jumped into action without really thinking about who it was he was saving. His first impulse could have been just to stop a potential disaster from happening on the pitch.
One possible reason could be that he felt he had learned enough magic to face his enemies on his own. He might have thought that the traditional Hogwarts education was too slow or not relevant to his specific needs, like dealing with Voldemort. Another reason could be some sort of conflict with the Hogwarts faculty. Maybe he didn't agree with their methods or decisions and decided he was better off without their rules.
Maybe he's falsely accused of stealing important Gryffindor artifacts. For instance, if the Sword of Gryffindor goes missing and Harry is wrongly blamed, the house might decide to kick him out. It could be part of a plot by a jealous student or an outside force trying to disrupt Hogwarts.
It could also be due to extreme exhaustion. Harry often gets involved in intense battles or has to endure long periods of stress. For example, if he's been fighting multiple foes continuously without a break, his body and magic might give out, leading to him passing out.
One reason could be to find peace. After all the chaos and war in England, they might just want to get away from it all and start fresh somewhere else.