Ok, so I checked out the link you provided a little more, and this time I also checked out the trends at another school (uiuc) to test your theory. Well, the same thing shows true. Over the years the staff has also adjusted in a very similar way at both schools in most departments. So this doesn’t explain how Michigan does it without having caps. Why does one school require caps and another school that measures just about the same in rankings and other aspects, not require caps?
As prospective students, knowing there’s no caps, why doesn’t every prospective CS student in the region go there, knowing they can get CS at a great school without competition? (Because the university has no idea if 100% of their applicants will choose CS). There has to be some kind of internal check. The 2.0 requirement isn’t it, because that applies to any/all engineering majors. So you can’t choose ANY major without that 2.0. So that may kick students out of COE as a whole, but not help balance the departments within COE.