Obsolete humans.
There's always an assumption in automation... That the workers displaced can be moved "up" to "more skilled" jobs. Certainly many can be. However, there are those that can't be, as well as those that don't want to be. Not everyone wants to be a CEO. Some people really do fit on the assembly line. They may not love (or even like) the job, but they may be even more unhappy being trained and moving to higher responsibility/higher stress jobs.