You know- I hear this said a ton- and I completely agree. The world has some amazing places- namely the history.
That said- The United States is the 3rd largest country in the world just behind Canada and Russia (who take the titles due to their frozen land masses). There is so much to see in our enormous country that you couldn't possibly see it in one lifetime. Heck- you couldn't really even see all of Adirondack State Park in one lifetime.
Not to mention that just in terms of geography/ecology, the US is one of the most diverse landscapes on the planet.
In any case, what you've been reading here is a lot of residue from the late-20th century notions of middle-class American values. The middle-class that statistically no longer exists, yet a surprising number of people still believe themselves to be part of. Some would categorize themselves today as "upper-middle-class" - but in the current economy is more aptly termed "beginner-level-upper-class".
It wasn't until the 70's/80's that even domestic air travel really became within reach of middle-class Americans for recreational purposes. Before that, air travel was for necessity only, when it was an option at all. Before that, "family vacation" meant getting in the car and going camping for a week or, maybe a splurge on a cabin somewhere within a day drive from your home. That's why WDW came around at just the right time - to take advantage of this new market of middle-class consumers to whom domestic air vacations were becoming within reach.
EPCOT Center in particular was incredibly timely in this regard, as it coincided with the increased romanticism surrounding international air travel when it started trickling within reach of those on the higher end of the middle-class scale. Until then, going "overseas" almost exclusively meant you had served in the military, to the vast majority of Americans.
That's why WDW was really considered a cultural experience back then - while we can kvetch about EPCOT Center vs. Epcot, that's almost entirely about Future World. World Showcase, stagnant as it has been until very recently, is of a time where most middle-class folks were just starting to dream about visiting some of those places.
This morphed as we got into the 90's, and on until now, as the economic divide really took hold - fueled by the concurrent and astronomical rise of multiculturalism. This has led to the adoption of what was formerly only a notion of the very most upper-crust - the casual judging one's worth/life experience largely on how "well-traveled" they are (colloquially tied into the notion of people being divided by "people who have a passport" and "people who
don't have a passport /wink /wink").