1. Culture. Japanese don't like to sell or buy second hand. New cars, new homes, new everything any time they can afford it.
2. Build quality is garbage. The culture of tare downs does not promote better bulding quality so most just go with the old tried and tested approaches.
3. Too many architects and construction workers. I believe the jobs market is pushing for heavy marketing of new construction. People are being sold on earthquake safety standards but really, all those people need to earn a living somehow.