It's not that the students need to be taught high school or college math in Junior high. It's that a teacher which did not master high school and college math

It's not that the students need to be taught high school or college math in Junior high. It's that a teacher which did not master high school and college math is not necessarily a good candidate to teach high school or advanced middle school math, and it absolutely occurs when the primary focus of the teacher's college career was teaching and not Math or another STEM field. The model in the US seems to have become that the Teaching degree is the most important degree for a public school teacher regardless of the subject that is going to be taught. At some point that breaks down in a big way in the STEM fields in the range of middle or high school. Certainly you are not going to be taught Math at the College level by someone who does not have a Math degree. But in public school they've decided at some point that a math teacher doesn't need to have a math degree.