I think this is because in Japan there still is more demand for film and therefore launching a film product is less risky economically speaking. When you make a new product you must spend money in a launch campaign, you must convince dealers to stock it in quantities that make sense etc.
I think this will slowly change in the future, when internet retailers such as Amazon will gain more importance for film distribution. I have already switched my purchases to online shops (not just for photographic supply I should add).
If you search Amazon you can find Fujifilm Natura Classica, or the cameras which I linked in my previous post. They are sold by a Japanese retailer or by Fuji themselves and delivered to your address. This might be a very interesting way to sell film (provided buyers accept the idea of buying 20 - 30 rolls at a time) and cameras. Imagine the risk for a shop in putting in stock a new medium format film camera. Online retailers have a hugely smaller inventory risk.