You forgot to mention one important fact: those who operate the schools, those who teach the teachers are usually persons who are by comparison with their old schoolmates and peers in the colleges and university, not well-educated. Probably 70% of the school administrators in Texas are former coaches, and while I think that most of them have more native intelligence and common sense than many who have taught academic courses, that means our schools are run by people who know little or art, literature, math and science. They are easily sold a bill of good by the peddlers of the latest educational fads. You know that a common joke among teachers is that the “reformers” keep rebranding ideas that have beeb tried and failed. School administration is a kind of appointive politics, and even the largest of school systems are run by people who have run out of new ideas.
While I can't speak to how decisions are made in the various states and counties with respect to selection of curriculum, I can state emphatically that principals in the districts I have worked in DO NOT select curriculum materials. That is done at the district office level by a curriculum committe, and then the final say goes through the elected school board. Classroom teachers and principals are rarely even asked for their input.