How the fuck they got "good credit" IN AMERICA, and they all the fucking way in China working with the Yuon[sic]? you moron!!! DO YOU HAVE GOOD CREDIT IN CHINA??? IDIOT! HELL NO YOU DON'T
Their credit ratings don't translate over here, stupid. and 9 outta 10 Japanese ain't rich like that to have good credit when they land on American soil, so what do they do...
Hey, stupid, when you have a large bank account, a high-paying job and are sponsored by a large multinational corporation, banks consider you (or your company) a good loan risk. If I have a large bank account and the backing of a large multinational corporation sponsoring me to work in China I will be treated accordingly (there are different types of visa status in China and the personal credit rating doesn't really translate exactly).
You are confusing all sorts of different immigrant experiences. If you see 'wealthy' Japanese citizens in the US, they are probably here for a limited amount of time on an H-1b visa, having been transferred by the large multinational they work for back in Japan. Some may be visiting scholars or artists. The large houses you keep peeping into are most likely most often those of US CITIZENS who are 2nd or 3rd generation and have achieved success through hard work and self-sacrifice. If you go to a private high school and see a bunch of Korean students, they are most likely here on student visas and living away from their parents and working towards a very specific goal under rather specific expectations. Nonetheless, they are still kids and will do a lot of the ill-considered things that American kids do when circumstances allow. If you notice 'ethnic group X' running a nice restaurant, it was probably financed by generations of one family, or a community, pooling all their resources to work together, sacrifice, and make the most of opportunity found in the US. If you go to an inner-city public school and see a bunch of 'Asian' kids, they are most likely the children of actual immigrants, most likely Khmer speakers, and most likely trying to get by under trying financial circumstances (as well as other challenges).
There is no monolithic immigrant experience, and no grand conspiracy that can justify your prejudice and paranoia, you freak.