That’s because the rice sold in Japan is generally the highest quality, so it makes sense that it costs more than the rice exported overseas to places like American supermarkets and Costco. The rice you see in US stores is usually a lower grade than what stays in Japan, though not necessarily “low quality.” Japan has historically been pretty selective about what gets exported versus kept for domestic consumption.

There’s also been a rice shortage/crisis in Japan recently, which has pushed prices up even more. See here → https://www.borgenmagazine.com/japans-rice-crisis/ and here → https://old.reddit.com/r/japan/comments/1kthwmr/e/

I would guess that rice is also a lot better quality

Surely also restaurants and larger vendors have ways to buy rice in bulk in Japan - maybe they just don't have the American version for of this for consumers ? Sort of like how in the US people can go to a restaurant supply store (but often dont)

tariffs made Japanese rice farmers lazy.. just drop it and Japan will go back and eat rice