Because it might send the stench and noise of other people and may cause dirt on the classroom.If not, eat in the classroom to make the classroom clean and odor.
You could smell the classroom and can interrupt other people's dirty classrooms and could not eat in the classroom to make the classroom clean and not smelly.
It may smell in the classroom and distraction of others and may make the classroom is dirty.If you don"t eat in the classroom to classroom clean and no smell.