These people come from universities where they usually had the lowest SAT scores and would not have earned any degree if they had not gone for a teaching degree.
Our entire education establishment is predicated on job retention and deliberately hiring the dumbest people to keep them beholding to the teachers unions and their overpaid hierarchy.
Also, it is easier to lead a bunch of ignorant people (our students and current graduates) around by the nose than to lead people who have been taught to think for themselves and have been given the tools to do so.