Well, isn't part of the reason because R&B stopped being the trend in Japan a long-time ago? I mean, yeah, you still get some who do that and mix it with pop (Kana Nishino, Kuu, etc.) but for the most part everything popular in Japan now is either idol pop, boring ballads/adult contemporary, K-Pop, or electro-sounding (and even electro trends have died out save Perfume, capsule, and possibly Kyary).
I think Japanese people still associate CK with her prime time days (when she was doing heavy R&B influenced music and not pop) and therefore just aren't interested in her image (which is a little prejudiced but Japan is).
