Consequently, employers simply do not have the "luxury" to set up a system that treats employees as disposable. It's not profitable at all to do what you indicated is being done, as the cost of finding, hiring, and training new employees is considerable. That's why, so often, you see businesses doing the opposite of what you describe by holding on to poor performers far longer than they should - dealing with worker incompetence is sometimes preferable to starting over hoping for a different outcome.