its because in the us phones are almost always on contract (phone and plan come in a bundle) and the carriers simply dont have nokia phones available.

If they do have a nokia its not usually one of their top phones ...the last nokia to be available here was a c7 and now the lumna 700. Nokia really sucks at marketing and making deals with US carriers.

The 4 major carriers are split att and tmobile are gsm and verizon and sprint are cdma.

edit btw i havent done much international traveling but here in the US recently I have had a lot better luck going directly through the airlines rather than travel sites. Then again there are only a handful of airlines that I will fly on.