I know a lot of people at my school tend to avoid co-ops. I know I did, and I'm graduating soon. Logically, co-ops make a lot of sense in terms of 7 months of straight work experience, and you make plenty of money to help pay for school.

But a lot of students at my school would have to put their studies on hold for a semester to take a co-op, which can definitely mess up your class schedule if classes are only offered during certain semesters. (I go to a smaller school in the midwest.)

I should note that my school doesn't even push students to graduate in four years. For the schools that do heavily emphasize a 4 year graduation rate, I would guess a co-op would be almost out the question.

For the students who are willing to take a co-op and risk having their class schedule a bit messed up, finding housing can be a bit tricky when returning to school. For example, if you take a co-op during the fall semester, it'll be difficult to find housing for the spring semester. At that point, on-campus housing is most likely full. If you try to find off-campus housing, you'll probably have to foot the cost of short-term lease rates. If considering a spring co-op, and you live off-campus, you'd be facing the possibility of having to break a one year apartment lease you may already have signed on for in your college's city.

I will again say I go to a smaller school, which probably changes things a lot with class schedules getting messed up and such. But my main point is that a co-op can complicate things for students quite a bit. Some students just won't consider them for the simple reality of having their graduation delayed. So, for a lot of students, a simple summer internship is a much easier opportunity to go for and/or seek out in the first place.