These are mathematics textbooks widely used in elementary schools in Japan. Can you see that it is considerably thinner than American general textbooks?
Japanese textbook publishers place importance on making students deeply learn important topics that are carefully selected, rather than cramming textbooks with many topics. We consider "efficiency" in education programs are what Japan boasts to the world. This enables teachers to concentrate on the problem of "how to teach" without getting concerned about "what to teach". Students are given the opportunity to think about many things that are helpful in understanding mathematics with few pages.