part of an account I heard of this somewhere else was that the turnover of employees was specifically between car manufacturers. Because they all paid more or less the same, if a worker got annoyed he would leave with no notice and go to a competitor.

Ford also refused to re-hire anyone who had previously quit, so the $5 was a great example of "Golden handcuffs". People would think twice before leaving, knowing they would be making 50% for the foreseeable future if they did.