I travel abroad semi-often, I lived abroad (like some American college students who spend a semester abroad while in college), and many people around me do so for the excitement of exploring new cultures, regions, places, etc. But there are people I know who don't travel abroad because:

1) Money. The United States is a large country and fairly far from other places. Getting to nearby foreign countries (Canada and Mexico) can easily be a $600 flight. Getting further (Europe, South America, Asia, Africa, Oceania is even more expensive).

2) Lack of vacation time/PTO compared to other developed countries. Americans often get 2 weeks max of paid time off and a trip far away requires at least a week to be worth it. That would only leave a week for occasional days of (taking a day of for your birthday, a long weekend trip, holidays, weddings, funerals, etc.)

3) Disinterest or dislike of cities/urban areas. This is rarer but exists. I know many folks who think we have enough interesting things at home and would rather drive to a U.S. National Park than go to a large city with a large airport and fly to a foreign large city/airport where everything is unfamiliar. I see that in family from rural places that would rather go hunting.

4) Fear. I find this among the same crowd as #3. I know people who straight up refuse to go to Mexico, even if it's in a very safe heavily tourist resort area like Cancun because they fear they will be kidnapped or hurt. That same crowd paid a lot of attention to knife attacks in London. I don't mean to get political, but I think some people have an outsized view of violence in other places and would rather be safe and at home.

A desire to live abroad and emigrate is a lot more rare. Of those who travel, like myself and friends, we occasionally dream of living abroad for a few years. We could have a higher quality of life with more vacation time (and nearby vacation opportunities), starting a family or raising kids could be easier in a place with a bigger social safety net, and some Americans who dislike certain political parties jokingly consider moving abroad to get away for a few years. However, I only see that "live abroad for a few years" among upper middle-class people who have options. I don't often see that on less well-off people who are just working to survive.

Very few Americans emigrate. I only know a handful of people who have and that's because:

1. Work or Family. Maybe they joined a company based in Australia, Canada, or France (some other industrialized and developed economy) and career wise it made sense to move. Maybe they married a foreigner and ultimately chose to move/start a family in a different country.

2. Cost of Living. This is really for retirees who want to move abroad where the pace of life is slower and they can live comfortably on their savings. Often it's Mexico or the Caribbean. This is circumstantial and most Americans don't "dream" of that from a young age.

3. Obsession with a foreign country or ideology. This is exceptionally rare but I know someone who is obsessed with China and communism and plans to do a Masters there, get a job there, and fully emigrate.

To sum it up, many Americans do dream of traveling abroad but those who want to live abroad often do so only for several years before returning to the US. Those who genuinely wish to relocate and settle abroad often do so circumstantially and its uncommon.