I got schooled by 7x World Cup winner Tomoa Narasaki (youtube.com)
Japan dominates boldering. Other countries are physically stronger than Japanese, so they try to find other ways, such as thinking about small details, speculated Tomoa Narasaki. ... It's also possible they have a low center of gravity, are lighter and more agile, and the sport may attract Japanese, being non-confrontational and requiring a lot of personal involvement but little social stress, compared with something like basketball which seems to be popular in China. 
