Not all teachers want to teach at all grade levels. My sister specifically is an early childhood educator. She wanted to be a kindergarten teacher, but ended up working for a private daycare. There is no way she would teach high school. One she does not know those subject to teach, two as said she is an early childhood teacher.
My high school English teacher was moved to the middle school and ended up retiring because she was a high school teacher, not a middle school teacher, it was not her wheel house teaching children of that age.