I'm from southern California and there are a ton of bilingual/trilingual folks...you must be referring to the Bible belt region lol.
Southern California is one of the largest multicultural regions in the US. The term "Ugly American" has been around for a
long, LONG time. There's a reason that there's a joke about Americans claiming to be Canadian when they are overseas.
These days, there's definitely growing multiculturalism, but aside from states bordering Mexico and a few big cities, I'd argue that for a big part of US history there was next to no exposure to foreign cultures for most Americans. That, along with American exceptionalism that's led to paternalistic military and economic expansionism, hasn't given American or Americans a very good reputation. One argument I've heard about American outlook on foreign cultures is that the vast majority of Americans that have spent time overseas have been in the US military and often as occupiers, and often over either 3rd world countries/countries that have been devastated by war. Military guys that call Asian women LBFM (Little Brown Fucking Machines) probably aren't going to go out of their way to respect the culture or learn Vietnamese or Tagalog. Not to mention the usual American personal openness, which can be friendly and gregarious when it's the good, and annoying and disruptive when it's bad.
Yes, the Bible Belt (lol) is a core of monoculturalism, but so is most of the mountain west, the midwest, and a lot of the northeast, too. And as I said before, there's a lot more multiculturism now than when "Ugly American" was first coined. There's been a big rise in Hispanic population growth, and lately especially Asian folks of all stripes, from Middle Easterners to Indian subcontinent to Chinese and Koreans. When you can go into a city of pretty much any size these days and find good mexican food and any other kind of Asian food other than Chinese or Indian food, you're seeing some good change.
Although of course there's a pretty sizable percentage of Americans that are freaked out about this new multiculturalism and are threatening to elect someone like Trump or Ted Cruz (he of Canadian birth and Cuban heritage) into office. So the "Ugly American" moniker isn't going to die any time sooon.
I'm an American, but I don't think you nor I are average Americans, or even average Americans that go abroad.