They may miss out by rejecting a few who would actually attend if admitted.
If, for example, there were 100 such students, but past experience indicates that only 1 would attend, they could still admit all 100 of them, assuming that that would increase the number of matriculants by 1. One extra top student may be a better student than one at the lower margin of admission that they would otherwise have to admit.
This applies to any school that rejects “overqualified” students based on assumed low yield.