Most people are taught that in school. They don’t know how much teachers are paid but they “know” that teachers are underpaid.
“Underpaid” may have been an adjective that could have been applied in the 1980’s, but the contract then was to take the lower wage in exchange for a fast track to job security.
Once tenure was reached, it became practically impossible to dislodge a tenacious leech personality, regardless of degradation of teaching effectiveness. This made the demographic prime pickings for union organizing, whining about “poor pay”, and whipsawing various local school boards for more concessions and broader benefits, only one of which was “parity” in wages. Fact is, most of these “professionals” would have been bounced from one job to another for years before they would have settled into a comfortable position in terms of wages balanced against actual effort put in on the job.
The really poor teachers are “kicked upstairs” to a non-contact job in “administration”. And a raise in pay.