An old story:
"They are sanitized to avoid offending anyone who might complain at textbook adoption hearings in big states, they are poorly written, they are burdened with irrelevant and unedifying content, and they reach for the lowest common denominator."
A handy rationale:
Few elementary and high school textbook publishers "can afford to spend millions of dollars developing a textbook series and not have it adopted in these high-volume states," the Fordham Institute said.
American textbooks are both grotesquely bloated (so much so that some state legislatures are considering mandating lighter books to save students from back injuries) and light as a feather intellectually, flitting briefly over too many topics without examining any of them in detail. Worse, too many of them are pedagogically dishonest, so thoroughly massaged to mollify competing political and identity-group interests as to paint a startlingly misleading picture of America and its history.