On the backs of babes.
It seems since the scores are falling in international tests, and Japanese kids aren’t learning stuff you can test as much, there is a panic to find a solution.
About 10 years ago there was a move to restrict time at school because kids were not very well-rounded. They tend not to play together, or learn about cultural activities. To increase “humanity” among the kids, they were given most Saturdays off (yes, they used to go most Saturdays). The number of school days dropped from about 240 to 210 (the US has about 180).
The drop in scores on these international tests didn’t start appearing until about 5 years after the change. Of course, the first thought on the cause of the drop was the changed schedule. No solid indication of causation here, but everyone thought something must be done.
So what did the Ministry of Education come up with? Reinstate Saturdays, and double the page count of the textbooks. You see, the system here in Japan is incredibly centralized. There is a week-to-week curriculum that everyone in K-12 follows. So a kid could move from Hokkaido down to Kyushu over the weekend, and pick up exactly where he left off. (The textbooks might be different, the content is the same.)
So now the kids will be carrying much heavier backpacks, and the publishers fat and happy. There is a constant outcry when new textbooks are brought out, because of their (non) treatment of WW2 and things like the Rape of Nanjing. Now they will have twice as much room, but we can be fairly certain there won’t be twice as much content.