Because to THE UGLY AMERICAN the language they speak is the only one that is worthwhile and everyone who is anyone should LEARN it and speak.
They do not like folks speaking other languages in front of them. They get hostile and angry as if it is a purposeful affront to them.
Europeans in general learn other languages as part of their normal education. They don't think they're "hot stuff" because they do. They just think it works better to be able to speak the language of whatever country they visit. For one thing the natives appreciate it. Why are americans so rigidly defiant and certain of themselves in the that regard? I HAVE NO IDEA. Being pleased and proud of being too lazy to nearn another language and worshipping their ignorance seems weird to me.