One reason could be that they receive a call for help from a far - off place. They feel a strong sense of duty to go and assist, even if it means leaving the comfort of Camp. This call could be related to a group of demigods in trouble or a threat to the wider demigod world that only they are believed to be able to handle.
I'm not entirely sure as I haven't read it specifically. But generally, a novel about 'drifters' might be about people who are constantly on the move, perhaps exploring different places, cultures, or just living a nomadic lifestyle.
The 'the drifters girl' story is likely about a girl who has some connection to the Drifters. Maybe she's a fan, or perhaps she has a personal journey intertwined with the group in some way. Without more specific information, it's hard to say exactly.
Start with creating a character profile for the Naruto characters who will be in the Drifters' world. Decide how they will react to the new environment. For instance, if Hinata is in the Drifters' world, she might be initially shy but then use her Byakugan to scout the new area. Then, outline the plot, starting from their arrival in the new world to the challenges they will face.
In fanfiction, their departure from Camp could be due to a prophecy. They might be the only ones who can fulfill it. So, they leave the safety of Camp and embark on a journey filled with challenges. Along the way, they could face their inner demons as well as external threats. They might have to make difficult decisions that test their loyalty to each other and to the demigod community. This could involve choosing between saving a friend or following the path of the prophecy.
He might leave because of a personal conflict. Perhaps he has a falling - out with some of the other campers or with the camp leaders. Like if he disagrees with a new rule or policy that the camp has implemented which he thinks is unjust.