The cost of living is higher in Japan. The total size of the market is smaller.
I'm not sure this is the case. Astronomy is a popular hobby in Japan, compared to the US and Europe. Every university and high school has an observatory, almost without fail. I'm following a blog from a japanese amateur and he often reports from different astronomy shops in his area and boy, there's a lot of them! And lots and lots of well-visited, popular public observatories as well.
And since their apartments are often small, small to medium aperture apochromats seem to be the scope of choice. Especially since photography is immensely popular.
My gut feeling is that the market for apochromatic refractors is considerably larger in Japan, than it is in the US.