If you don't understand why universities accept more students than they can take, or why airlines overbook, you've probably never held a managerial position.

As the article states, UCI accepted 31,000 with the expectation that about 6,250 would actually show up. However, due to unforeseen economic factors and/or miscalculation, 7,100 indicated they were planning to enroll. That created a problem. 

If some university made you Director of Admissions, and you only accepted the exact number of students you could handle, you'd end up with only 20% of the students you really wanted. You'd be the laughing stock of academia, and your okole would hurt from the massive kicking they'd throw in while showing you the front door.

If you don't understand that, ask a smart friend to explain, maybe draw a diagram or something. Good luck! 👍🏼