This is the US we're talking about. A sizeable number of people haven't left their own state, let alone travelled internationally. Working hours are also incredibly long (a factor cited in why opinion polling wasn't catching Trump voters), so many people (particularly in some sectors) haven't got the time to be keeping up on current affairs.
Yes I think sometimes people forget that the US is a
continental sized country and many of the states within are as large as nation states. California for example has a population larger than say Poland, Australia or Ukraine and would be the fifth largest economy in the world. Florida has a population larger than the Netherlands, Chile or Romanian and would be the fifteenth largest economy in the world.
The is Big with a capital 'B'. It's hardly surprising that many people haven't travelled internationally, nor indeed have ever left their state, when you looking at a nation the size of the US.
It therefore really shouldn't be at all surprising that they just don't care all that much about what people think about the US internationally. Why would they when their country is as large as it is and as physically isolated from the world as it is?
Heck, even here in the UK our General Elections never really feature foreign policy that much. It's far more about domestic matters and concerns and we have none of the advantages that the US.