They could be afraid of the responsibilities that come with joining Beacon. Being a Huntsman or Huntress is no easy feat, and there's a lot of pressure to protect the world. RWBY might not feel ready for that level of commitment. Also, they might have some issues with the way Beacon is run. If they've seen or heard about any form of corruption or unfairness within the academy, that would be a big deterrent.
One possible reason could be that they have their own personal goals that conflict with what Beacon offers. For example, they might want to pursue a different type of combat training or they have a family matter to attend to first. Maybe they've heard rumors about Beacon that make them hesitant, like strict rules that would limit their freedom.
The story would likely focus more on their individual growth outside of the structured environment of Beacon. They might form their own small team and train in different places, encountering different challenges and allies. Their combat styles would develop in unique ways without the formal training of Beacon.
One reason could be his underlying sense of good. Despite his family's alignment with the Dark side, Draco might have a moral compass that rebels against the evil associated with the Dark Mark. He may have seen the destruction and pain it causes and doesn't want to be part of it.
It could also be due to a false accusation. Perhaps someone framed him for something he didn't do, like stealing important artifacts from the school. And in the world of RWBY, if he was found to be secretly associated with a group that the school considered dangerous, that would also lead to his expulsion.
Well, in 'rwby neo goes to beacon fanfiction', Neo could be exploring the Beacon Academy. She might be trying to find a place for herself among the students there. It's possible that she'll cross paths with the main RWBY characters and have some interesting interactions with them. For example, she could team up with them in a mission or have a friendly sparring session.
One reason could be that he's tired of being used by the gods. In many of his previous adventures, Percy has been sent on dangerous quests for the gods' purposes. He might feel that they take advantage of his skills and loyalty. For example, he was constantly in life - threatening situations just to retrieve some item or solve a problem for the Olympians. Another reason could be a personal grudge. Maybe a god has wronged him or someone he cares about in the fanfic, and he decides he's not going to play their games anymore.
He could bring new skills and knowledge. For example, his apparating ability could be useful in combat or for quick escapes in RWBY's dangerous situations. Also, his knowledge of magic could potentially be combined with the Dust - based technology in RWBY. He might start teaching some students about different forms of magic, which could change the way battles are fought at Beacon.
Well, one possibility could be that Roman joins Beacon under false pretenses. Maybe he's trying to steal some valuable Dust or intel from the school. He could pretend to be a reformed criminal, fooling some of the students and teachers at first. But as the story progresses, his true motives start to surface and the characters have to deal with the betrayal.
One possible plot could be that the characters are able to prevent the fall through better communication and teamwork. They might discover the enemy's plans earlier and work together to strengthen the defenses of Beacon. For example, Ruby could use her speed to quickly spread warnings, and Weiss could use her glyphs to fortify key areas.
One possible reason could be to protect his friends. Maybe he discovers a new threat that is specifically targeting him, and he decides to leave Beacon Hills to draw the danger away from those he loves. For example, in some fanfictions, a powerful and vengeful supernatural being might be after Stiles, and he believes that by leaving, he can keep his friends safe.
One reason could be that he feels betrayed in Konoha. Maybe some secrets were uncovered about the village's past actions towards him or his family that made him lose faith. So, he decides to start anew in Kiri where he hopes to find a different kind of acceptance.