It's also another reason why Admission/Acceptance Rate is a terrible, almost worthless metric in many circumstances.
Suppose School A and School B are good schools that have roughly similar admissions standards and generally good students apply to both.
But School B receives a ton of extra applications from largely less qualified students and then rightly rejects them, School B's Admission/Acceptance Rate will be significantly lower and it will look more "selective." But in reality, again, both schools are equally selective. You have to judge by the characteristics (scores/grades/achievements) of the students that do enroll, not the admission/acceptance rate.
Why would all the extra, less qualified students apply to School B and not School A? Maybe School B is in a bigger metropolitan area (*cough* UCLA) and/or has better name recognition for the less qualified students (e.g. due to past sports successes). Or maybe (as per above) they are intentionally recruiting candidates they have no intention of accepting to make their acceptance rate look better when in reality they are no more selective. But either way, those extra less qualified students in no way make School B more selective or harder to get into than School A.