Also, I suspect, so they can have some control over who leaves. When employees start leaving on their own, the first to leave are going to be the highly skille

Also, I suspect, so they can have some control over who leaves. When employees start leaving on their own, the first to leave are going to be the highly skilled but underpaid ones. They are attractive, relatively inexpensive to attract away, and have relatively little incentive to stay. They're also the ones the company most wants to hold on to, for similar reasons.