So, maybe a lot of the people who end up here are like me, they listened to Japanese music through the Internet, thought it was awesome and were left wanting more, only to find out that it is not available in the local CD shops (yeah, the World Music section has a very deceiving name) and it will cost you most of your earnings to import. So, why isn't J-POP exported around the world like American music is? I'd like to explain a few of the reasons why I think this is the case.
1. I've mentioned before that Japan has the number two largest recording industry in the world and the United States has the largest. Japan has reached this position through mostly domestic sales, while the US has secured its place through its global appeal. Basically, there is a very large Japanese population to target with a very strong domestic industry, which eliminates the need to expand to foreign markets.
2. A lot of effort goes into promoting each song and album within Japan, including appearances on music shows, tours, concerts, etc. A lot of time and effort is spent on hooking the local audience, so there's not much time and effort left to try to break into foreign markets.
3. Most audiences are not very accepting of music that is in a foreign language. Some people find it difficult to relate to songs which they don't understand the lyrics and people who are unfamiliar with a particular language may not find its general sound system aesthetically pleasing. Japanese artists also tend to fall into line with the rest of the Japanese population in the sense that English is not really their strongest subject. So, producing all their songs in English could be quite a hassle and not necessarily effective.
Here's an example of a song entirely in English by a Japanese band.
Lyrics can be found here: http://j-lyric.net/artist/a000673/l00d722.html
4. The J-POP method of marketing is very foreign to the Western world. In the States and other countries, there are actors turned singers and vice-versa, but nothing like the multimedia entertainer which is the idol. Actually, J-POP does enjoy some popularity abroad, but mostly in East and South-East Asia, where Japanese popular culture has always had a big influence, so the whole-package deal is more accessible, rather than just the music.
I'm not saying that there are no fans abroad. There are many fans of Japanese music in North American and Europe, but they make up a fairly limited sub-culture compared to the whole. I think a lot of the reasons I have provided above explain why Japanese music doesn't seem to reach out to foreign audiences as much.