CWRU - Four-year Graduation Rate

Does anyone have a sense of why Case Western’s four year graduation rate is just 67% or thereabouts. That seems low given the high quality of kids who go there. A curious anomaly?

I know a lot of engineering students do the coop year- so that adds at least a semester/year to getting the degree (but they get paid for it). My daughter, who is a CWRU junior, tells me she does not know anyone from her freshman class who is still not a student there.

The co-op explanation makes sense. I noticed that Carnegie Mellon also has a slightly lower four (and six for that matter) year average than one would expect and thought it might have something to do with the difficulty of the subject matter that a big chunk of the students at those schools pursue. I also wondered whether it might be tougher for the higher than usual international cohort at those schools to get out in four years.