It's not just Americans who do this by any means, and nor are they the worst offenders! Trust me on this, I'm British - the most wilfully parochial nation on earth.

You'll always get the odd jerk, but mostly this stuff tends to come from a lack of travel experience more than anything else. Unless you've travelled, you may not even realise what assumptions you're making about how day-to-day life works. And, well, a lot of Americans haven't travelled much outside of the USA. (That's not a criticism by the way - the USA is absolutely enormous and incredibly diverse, and you could spend a lifetime exploring it and not see it all.)

All that said, back in the days before dual voltage power supplies were common I did used to find it amusing watching Americans in Europe blithely plugging their electrical goods into the 220V mains and wondering why they blew up.