Originally Posted by jayeff

Your own cultural perspective is the main reason. Nothing creative is bound by absolute standards set in stone, common to all people. Music which jars your perception will be entirely familiar and enjoyable to someone else. If you were running a non-US record company, you would likely hope that one of your artists will get an international break, but you are not usually going to record people who simply put out US-style music in their own language (not even when that language is english).

You are also overlooking the reality that even were you to confine comparison to english-language sources, a heck of a lot of music stays on one side of the Atlantic or the other, never successfully making the crossing. Same reason.