Korean girls are quite beautiful. In the U.S., we don’t get many Japanese providers. If they barely serve gaijin in Japan, there’s even less incentive for these beauties to work outside of Japan. The Asian providers we do have here are mostly Korean or Chinese. Occasionally Korean and Chinese girls try to pass themselves off as Japanese to the uninformed. It works in metro areas in the US with low Asian American demographic numbers.
You Japanese providers know you can make a good income if you ever relocated to America? Of course in America we do expect FS, and the sex business is not quite legal, so I imagine this could be a problem for recruitment.