Maybe it's out of envy. He sees Hermione's abilities and popularity and wants to possess her in a way. He might think that by forcing her to marry him, he can somehow be part of what she represents in the wizarding world.
Maybe Draco is jealous of Hermione's intelligence and abilities. In the fanfiction world, he could think that by making her his wife, he can somehow take credit for her achievements or keep her from outshining him. It could also be a power play. Draco might believe that having Hermione under his control through marriage would give him more influence in the wizarding world, especially if she has connections that he wants to use for his own gain.
One possible motive could be jealousy. Hermione is highly intelligent and often outshines Draco in academics. In a twisted version of a rivalry, Draco's envy could turn into a deadly hatred. Another could be his family's influence. If the Malfoys push him to take extreme actions against Muggle - borns, Hermione would be a prime target.
One consequence could be a huge rift among their friends. Harry's friends would surely be against this forced union and might try to rescue him. For Draco, his friends might also be divided as some may not support such a cruel act.
One possible reason could be his over - protectiveness. Edward might think that marriage would legally bind Bella to him and he could better protect her from the various dangers in their world, such as other vampires. He may believe that as his wife, he could keep a closer eye on her.
She would most likely be furious. Hermione is a smart and independent character. She would immediately start planning her escape. She might use her knowledge of magic to try and outwit Draco.
In some fanfiction, if Draco forces Hermione to marry him, it could lead to a very dark and complex storyline. Hermione, being a strong - willed character, would likely fight back in some way. Maybe she'd initially resist and try to escape. It could also involve other characters like Harry and Ron coming to her rescue. However, some fanfic authors might explore a more nuanced relationship where over time, Hermione might find unexpected understanding or even a strange connection with Draco despite the forced start.
One possible motive could be Bellatrix's loyalty to Voldemort. She might think that by kidnapping Hermione, she can get information about Harry Potter and the Order of the Phoenix. Hermione is known to be very intelligent and Bellatrix could believe she has valuable knowledge. For example, Hermione might know the location of Potter or the Order's plans against Voldemort.
Maybe Rowle is under the orders of a more powerful dark wizard. In the world of Harry Potter, there are always those higher - ups in the dark side who might want Hermione for her knowledge of magic, especially things like ancient spells and magic theory. So Rowle could be tasked with kidnapping her for that purpose.
One possible motive could be to use Hermione as a bargaining chip against Harry Potter. Since Hermione is his close friend, the kidnappers might think they can force Harry to do something, like give up a powerful magical item or valuable information.
One possible reason could be that Sasuke is trying to protect Sakura in his own twisted way. He might think that by making her his wife, he can keep her safe from the dangerous world they live in. Another reason could be related to his family. He might see marriage to Sakura as a way to rebuild his family name or something similar. However, his method of forcing her is completely wrong.