The US and Canada (outside of Quebec, and partially even inside Quebec) gained the core of it's culture and language and the largest portion of it's early settlers from Great Britain, with France, Germany, and other NW parts of Europe providing much of the rest. Most of Latin America got it's language and culture from Spain and Portugal. And those nations were enemies or at least rivals) for a very long time.
So while the US later had substantial numbers of immigrants from virtually everywhere in the world, the Great Britain/NW Europe connection was the one most firmly established nationally.
As far as the travel is concerned, Americans are a little insular, and so have a tendency to stay home. But Americans can and do travel everywhere in the world. The other factors are cost and proximity. It is expensive and takes a lot of time to go to another continent. And since we have so much variety of places to go and things to see here, for many people foreign travel isn't as appealing.
