Karla Bravo comments

It's because 1) Japan is a self sustainable market. They sell so much in Japan that a lot of labels are not interested in going abroad. The few bands that venture to Europe, America or South America gather small venues mostly an attendance composed of several niches (jpop, jrock, anime fans)...

2) Japanese labels are very hard to work with, Kpop spreaded like wildfire basically because a lot of videos and songs are on the internet on official channels, Psy was on iTunes very easy to get popular with million on views on YouTube. Try to do that with a Japanese band, most official Youtube profiles have they videos locked for only Japan.

Of course there are a lot of talented musicians L'Arc en Ciel, X Japan, Scandal, Dir en Grey, Girugamesh but to make it in the US is very complicated because 1) Language is a big barrier (don't say no, americans would rather watch a remake of an European or Asian movie than watch it in the original language) 2) You have a huge competition with Big names, bands and pop stars.