It’s good old-fashioned xenophobia and is by no means unique to Americans or English-speakers even in the modern era. Anyone who has spent enough time in certain parts of France, Italy, or Belgium has probably encountered it at some point.
It’s everywhere but it is probably most prevalent in countries with a strong nationalist core and, in my opinion, ironically occurs most often in countries that have really fucked around with having an empire in the last century or so.
I don’t know about you all, but I have been posting as an adult human male for a numbers of years now despite being a 4 year old Alaskan Malamute. No one seems to notice or care.