They aren't more valuable, they just have a better bargaining position due to availability of other high paying jobs near them. The value an employee generates

They aren't more valuable, they just have a better bargaining position due to availability of other high paying jobs near them. The value an employee generates doesn't directly determine their salary; it is more of an upper-bound. Their salary is mostly determined by what the employer's next best option of employee is and what the employee's next best option of employer is.