According to the following article from the Huffington Post American people don’t travel much internationally for a number of reasons such as:
We have so much to offer in our own country This one is easy and is always my first line of defense. The U.S. is one massive country. Not only is it gigantic, but it is diverse.
We have extremely pricey passports Obtaining a passport isn't exactly cheap. At $135, we have the fifth most expensive passport in the world. That may not seem like a lot to some people, but keep in mind that takes 19 hours of work at minimum wage.
We aren't given vacation time The average amount of paid vacation time is two weeks. According to Forbes, the United States is the only advanced economy that does not require employers to provide paid vacation time. To make it worse, Forbes explains that nearly 1-in-4 Americans do not receive any paid vacation or paid holidays.
We don't use our vacation time That's right, the nearly 3-in-4 Americans that do receive paid vacation time fail to even use it! Oh my, are we that committed to work that we can't even take some time to enjoy ourselves?
We think you have to speak the language The only language I can speak fluently is English. It's embarrassing and I hate to admit it, but it does get me around the world.
Other sources appear to support the same view, as psychology.com for instance:
On a different note is The Telegraph which says:
But do not be deceived by the relatively low percentage of US passports holders. For the 42 per cent that do have passports use them - and frequently. One in five of all long-haul travellers has a US passport.
Are Americans far less likely to travel to foreign countries that the residents of other comparable western countries?