Japan is advanced in Electronics and Robotics, and they don’t have the same environment for money markets, and investment banking that could provide capital to Bitcoin and cryptocurrency start ups.
You are wrong about Japan its economics. They do have a huge huge market and they have amazing big companies that not only grew huge in Japan but grew big internationally, there are only a handful of nations that have companies that make 1+ billion dollars a year in profit, USA has a lot, European nations have few nations like UK, France, Germany and so forth, Japan is one of those nations and they are very big on finances because of that, since it allows them to actually end up handling tons of money, you can't just ignore it when you reach those levels.
This is why bitcoin was so big the moment it started in Japan, and this is why they had laws and regulations the moment it got some traction, while rest of the world was just watching Japan was getting legislature ready regarding crypto, hence why it could always be hub of bitcoin, but when USA is so much richer than everyone else, usually they take that spot.