Oh Seneca, some Britons are insular, and some Americans are insular. Plenty are also ignorant about others in their own country.
But not everyone and that is why sweeping generalisations are offensive. These are both big and diverse countries. We each have different experiences. I have worked in the US and in France and Germany as well as Asia, I speak five languages, my son studies in the US and my daughter spent her gap year working there and in France, my DC went to schools where only a minority of parents would have been British born, and indeed DD wound up near fluent in French from hanging out with kids from the Lycee, whilst DS was the only Brit out of 40 on his Masters degree in London.
Its cool, though I have a slightly concern about the extent to which they really understand how atypical a Central London childhood is. There is an analysis that describes people as either "anywheres" or "somewheres", and part of my concern about the EU is that it is run by Brussels' "anywheres" who fail to understand Europe's "somewheres". I have a great Fb feed with lots of articles posted from all over the world and a long standing subscription to the New Yorker (I love New York) but have spent much of the last decade working with carers, and tradespeople as I looked after a parent living with dementia. As a result I am often astonished at how little Londoners can understand their own countrymen and how easily they seem to despise them. I would see Brexit, and the recent election, not as anti-immigration but a protest vote against power cliques who seem to see themselves as entitled to run the country.
I could equally ask whether Americans understand America. DD reported that the parents of many of her American friends voted Trump, and a friend of mine confirmed she was probably right, though of course no one says so. My friend suggested that Trump was the master of the single issue. He offered action on a number of things that matter to specific voters (tax breaks which appealed to London's international rich, being one example) and which brought in the votes. He deals in transactions, not ideology.
My friend also suggests she is confused by the US/UK divide on Meghan. (She and her husband decided they would have been in London too long when they started to understand British humour. She now gets it and accepts that she is now probably here for good.) American friends and family were very pro-Meghan. The British were clearly beastly racists. It appears very different through a British prism.