Most college kids and a lot of high school kids use their summer vacations to work. There are a lot of students who would be unable to afford to go to college year round.
And as a recent college grad who is now working full time, all year round, in many ways life in the real world is easier than life in college. The few vacations I do get are real vacations, unlike in college, when I spent them working. Also, when I get home from work I'm done for the day; I don't have homework to do or papers to write.
Good point that school is essentially two jobs....one in the classroom and one for homework.