No it isn't. It's just that we have a huge country stretching from the western pacific ( guam, hawaii, etc ) to the arctic (alaska ) to the caribbean ( puerto rico ). We have a variety of cultures, regions, natural wonders and peoples than any country in the world.
Most americans can afford to travel overseas. But we have so many options within the US and its more convenient. Traveling from NYC to hawaii is far more impressive than traveling from NYC to London. And we have the grand canyon, mount denali, yosemite, yellowstone, florida, mount rushmore, new orleans, texas, chicago, endless list of places to visit. Most people, not just americans ) would explore their own nation first and then see the rest of the world.
It's generally europeans who brag about traveling and yet they mostly travel between tiny european countries. What's so impressive about someone in luxembourg traveling to france, germany and belgium in an afternoon? It isn't that impressive. But they could claim to have traveled to 3 countries even though those countries are pretty much the same as luxembourg.
To put this into perspective, the distance from moscow to berlin is 1100 miles. The distance from NYC to LA is 2700 miles. We just have a lot more land, lot more culture, lot more places to visit.