Hourly workers (unskilled labor) are flexible and cutting hours is almost as easy to reverse as it is to do in the first place. Cutting salaried employees (skilled labor) is a much harder and expensive decision to reverse. So doing so means that there is either a consistent issue that is not getting resolved, thus making them not worth the expense, or things are about to get so bad that the company feels that the savings are worth the loss of skilled labor.
And clarify the difference between skilled and unskilled labor (which might make this make more sense), this is not a description of the work itself, but rather the barrier of entry. Anyone can be taken off the street and trained into an "unskilled" position with relative ease. That is not true for "skilled" positions though. Which is why Amazon's decision to start cutting corporate jobs represents a fundamental shift in their path going forward.
