In some fanfictions, it could be a result of some magical influence. Maybe there was a spell or a charm that made Harry act this way. Or it could be an expression of deep - seated emotions that Harry has been suppressing for a long time. This action then becomes a way for him to break free from his self - imposed restraints and reach out to Draco in a very physical way.
Perhaps Draco realizes that Harry is in a dire situation where he needs the wand to save the day. Draco, having a change of heart, decides to give Harry his wand as a way of contributing to the greater good. This could be related to a looming threat that only Harry can face, and Draco understands that his wand can be a crucial tool for Harry.
One possible reason could be their long - standing rivalry. Draco has been taught to dislike Harry from a young age due to their family differences. His pure - blood supremacist upbringing might make him reject Harry as a mate because Harry is seen as a 'Mudblood - lover' in the eyes of Draco's family and their circle. Another reason could be fear. Draco might be afraid of what the wizarding society would think if he accepted Harry as his mate. The wizarding world has its own set of norms and expectations, and a relationship between them would be highly unconventional and likely face a lot of opposition.
Perhaps Draco has developed a sense of respect for Harry over time. He might have seen Harry's courage and determination up close and decided that Harry is worthy of his help. Throwing the wand could be his way of showing that he acknowledges Harry's importance in the fight against the common enemy.
Perhaps in a parallel universe where the whole wizarding world is different. There are no enmities between the Slytherins and Gryffindors from the start. Draco and Harry are friends, and Draco sitting on Harry's lap could be a common occurrence during their friendly banter or while sharing secrets in a cozy corner of the Hogwarts library. It could be a sign of their deep - seated friendship and trust.
A possible theme could be forgiveness. Harry might be in a position where he has to forgive Snape for all his past misdeeds. And this rather strange act of Snape bouncing him on his lap could be a catalyst for that forgiveness. Additionally, it could also touch on the theme of growth and change, both for Snape, who is showing a different side of himself, and for Harry, who has to adapt to this new side of Snape.
One reason could be for a disguise. Maybe he's on a secret mission and needs to pass as someone else. Another could be peer pressure. His friends might have dared him to do it.
Maybe Draco says some really mean and hurtful words to Harry. For example, he might make fun of Harry's family situation, like his parents' death or his relationship with the Dursleys. Words like that can be really cutting and could easily make Harry cry.
One possible reason could be his father's strict and cold parenting style. Lucius Malfoy was often very controlling, pushing Draco to uphold the family's pure - blood ideals and reputation, which might have made Draco feel suffocated and resentful. Another reason could be that Draco witnessed his father's dark deeds in the wizarding world, like being involved with Voldemort, and he might have moral objections to such actions.
One reason could be to add drama and conflict to the story. Fanfiction writers often like to create complex situations to make the plot more interesting. Another reason might be to explore different aspects of the characters' personalities in a non - traditional way.
In fanfiction, their kiss might be a way to break free from the expectations placed on them. Harry is always seen as the hero and Draco as the villain's sidekick. By kissing, they are defying those roles and expectations. It could also be a way to gain power over each other in a different sense. Instead of the usual power struggle based on magic or family name, the kiss becomes a new form of power dynamic between them.