A resignation is a bad negotiation argument.

If somebody wanted to stay, they should have negotiated earlier (be they boss or employee).

If a boss wanted an employee to stay, they should have appreciated that employee earlier. The reaction of the boss is flawed - wanting to negotiate with the employee who wants to resign.

Many things push a person to make the decision to start looking for a new job. Salary is only 1 of them.

A resignation is a bad negotiation reason/argument.