They should not be forced to do what they don't want to do. They might have something better to do. They might not want to stay after school. They might have to work at home.
Another reason is that they might have something better to do. People in school might have to do work at their house. Some of the people have jobs and cannot stay to do activity. They might have to stay after school and do school work. After all some of these kids might not want to stay and do activity.
Lastly he or she might not be able to do it. Kids might have a broken limb.