This isn't true. And I have an MBA, so I know that even if it were true, it's not what managers are being taught. It's expensive to replace people. Advertising

This isn't true. And I have an MBA, so I know that even if it were true, it's not what managers are being taught. It's expensive to replace people. Advertising, screening, interviewing, induction, training, all take up time. New employees are not productive from day 1, and take a long time to ramp up to "full" productivity. Losing people is also disruptive to the social life of the business - that person's friends may be less happy/productive after they leave. And all their friends may question their choice of employer - the loss of a popular staff member can trigger a wave of departures. And experienced employees are more productive. The economics of paying experienced employees more works fine.