Public school teacher salaries do not usually adapt to market conditions on an individual basis like in other industries. If you needed to pay like $5k more to get a new hire, for example, you would have to update the pay schedule to pay potentially thousands of teachers each $5k more. That cost can be infeasible in the short term. There are also non-monetary considerations. If your city is known for terrible working conditions, teachers might refuse those jobs even if your pay scale is competitive.