Why most textbooks in the same subject teach the same material & views? Take any random english textbook in medicine, biochemistry, statistics etc. you’ll see more or less the same structure. In non-english background, suddenly, contents & views may vary.
Example: in clinical physiology, english textbooks handpick a set of diseases (the same set) and present their underlying mechanisms. Non-english textbooks in physiology often focus on pragmatic real-life clinical issues like fever, pain etc.
Example: open any random english textbook in biochemistry, pathology etc., you can predict even the diagrams and the images you’re going to see. They’re copy-paste. But if you open a book, in the same subject, from Jaypee Brothers (India) you may see a different approach.
Textbook monoculture gives the false impression to students that there is such a thing that we call “science” which is solid and everybody agrees with. All medical textbooks present the same images on how lipids cause heart attacks & questioning this becomes a hubris.
The heart-bit of textbook monoculture is centralised examinations & credit transfer. US textbooks prepare students for SAT exams, USMLE exams (for doctors), bar examination (for lawyers), providing the “correct answers” for those exams.