For the last 20 years there has been a steady stream of articles on how Japanese web design is "broken", or "behind", or "cluttered".
There is also a steady steam of UI experts arriving from the US telling Japanese companies they need to modernize their look and feel.
The thing is, e-commerce sites like Rakuten are already heavily A/B tested and optimized. That graphic experience is common because it is most effective. Any analysis that does not focus on actual, observed user behavior is simply navel-gazing.
That said, the ubiquity of iPhone and Android UI is causing a shift in Japanese UI/UX design. People are becoming used to that as the primary interface.