Because that place no longer resembles the America they left. Because it doesn't include the daily stuff they prefer about France. Because back home people no longer understand you. Being international in the American mind-set is the ability of others to adapt to their way, as if it were not only the best, but essentially the only way. Expats visiting former homes end up feeling like complete strangers.
Expats are the true ambassadors of our age.
Try to use an American pay phone without an American calling card. Try changing a 200 FF note downtown anywhere other than an airport. International means the ability of getting Ethiopian food delivered quickly. It means the finding of great package trips to the Bahamas. It means selling your company's goods abroad without high import taxes.