The problem with CoCo Lee and Utada trying to cross over to the US was that they sexified their image too much...or at least they made their lyrics too demeaning. I think they would have had more succeess if they had stuck to their normal styles.
The sad fact about most Americans is...they just want the same old thing, the "Made in America" music. You see a lot of people in other parts of the world who give American music/other countries' music a try and they love it! Like, for instance, most of the Japanese I've met so far actually LOVE American pop and whatnot...it really surprises me. On the contrary, walk up to any random American in the US and ask them what music THEY like...you will most likely hear them say "I like [American] pop/rock/etc."
I know there are a lot of us here who actually do live in the US and love J-pop and such...but once you think about how many people are actually in the US, we're actually a minority.
Despite the US claiming to be a "melting pot," a lot of Americans are kind of closeminded when it comes to trying new music/foods/etc.