Japanese food is good, and since there are not many Japanese people around to open up Japanese restaurants, Chinese people step up to the plate.
Also, Japanese people aren't as flashy as Chinese people. They're all about being humble and such. So the few Japanese-run shops are often very small and personal. Chinese people are all about business ventures and getting customers--hence big fancy decorations and advertisements.
EDIT: Also, Chinese people ALSO know that white people can't tell the difference between Asians (in most cases). So if they mess up here and there culture wise, they know it won't matter to their customers.
*am Chinese, but know a lot about Japanese stuff. And my mom and I actually discussed this question years back.