The problem is they have several conflicting goals and education is only one of them. Secondary schools teach whatever their local government or state wants.

Historically, the US copied Prussian Frederick the Great's School system: https://en.wikipedia.org/wiki/Prussian_education_system#Unit....

Meanwhile the universities saw themselves as research institutions. They view teaching as a pipeline to produce future researchers. https://en.wikipedia.org/wiki/Research_university

When the states met and decided what high schools teach, they created Common Core which was highly controversial. https://en.wikipedia.org/wiki/Common_Core#Reception_and_crit...

Now there are things like UT Austin's online high school where they teach everything like Khan Academy. Again they are teaching to meet whatever standard the state told them to meet. https://highschool.utexas.edu/hs_courses