I did a quick check - to fly from Los Angeles to Santiago Chile (to pick a long-distance route entirely within the Americas) most every airline I noticed was do

I did a quick check - to fly from Los Angeles to Santiago Chile (to pick a long-distance route entirely within the Americas) most every airline I noticed was doing it in two hops (typically LAX -> Lima -> Santiago) with narrow-body jets, usually an A-321 or similar. If you were to leave from Miami, there are a couple of non-stops available, using either a 767 or 787. But the rest would have things like overnight layovers midway. So I agree with you - if the demand were there, then a US carrier would lease an A-380 or four, so that they get more fares for the same fuel.