It's cultural -- there is excessive NIH in Japanese corporate culture. They see using a framework as showing some sort of weakness. Managers are rewarded for reinventing the wheel.
This was my experience, too. Our CEO decided against the advice of all of our programmers that we should write our own CMS, primarily because he felt that it would put us at an advantage over our competitors to be able to say that more of the software that we used was written in-house. I left shortly afterwards.
