And if people are just interchangeable widgets, that's a clever strategy.
People aren't, though. The most valuable people are the ones who have the most options, precisely because they are valuable. If you play that game, you're going to differentially lose your most valuable people. That's not a smart move.
The assumption being made is the most valuable people can be replaced by a couple of “less valuable” ones by make them toil harder and re-learn all knowledge the valuable ones had.
People aren't, though. The most valuable people are the ones who have the most options, precisely because they are valuable. If you play that game, you're going to differentially lose your most valuable people. That's not a smart move.