People are also only fungible to a limited degree. Companies cancel projects, eliminate functions, and so forth. Especially in the middle of a large layoff there's often a limited appetite for finding a new home for someone who may be a high performer in the abstract but doesn't have a job any longer and may not be an ideal match for a position that already has someone doing it.

This is my experience. The last company I worked for that did layoffs while I was there was an example. None of the middle managers had any input in the firing decisions at all. They were just given a list of names by upper management. They were very upset about it, because they couldn't lay off people that were underperforming and were forced to lay off people who were critical or performed very well. Many of them said that it didn't appear that the decision-makers even looked at performance reviews, either. It appeared random.