There aren’t always. There are plenty of places that pay teachers well. The problem is that the qualifications for a school that pays really well are pretty much the same as the qualifications for a school that doesn’t. Schools that pay well have 1,000 applications and never any vacancies, so new teachers have a hard time finding a well paying job. Public school employee salaries are public information, so you can actually look them up.

Average teacher salaries in Massachusetts dont look bad to me. profiles.doe.mass.edu/…/teachersalaries.aspx

Obviously, it’s not universal.