[bigstrat2003]

I suspect it's because in the US, it all gets lumped together under the "Japanese food" category. I suspect the dishes being foreign in origin makes people less likely to consider them as separate categories.

I can confirm that I have the same thing in my part of the US though. A lot of restaurants will offer sushi and ramen both on the menu, with some other dishes like katsu curry showing up here and there. I would say the best sushi/ramen places here do specialize (just like you said about Japan), but it's pretty common to see places which don't.