Why Do American Flights Attendants Expect Everyone to Speak English?

To begin, a joke:
What do you call someone who speaks three languages? Trilingual.
What do you call someone who speaks two languages? Bilingual.
What do you call someone who speaks one language? American.

On my flights to and from Shanghai, I had the same crew. They were perfectly adequate, but I was a little surprised that it appeared as if only one of the flight attendants serving the economy cabin spoke any Chinese. And I’d say that at least 50% of the passengers were Chinese, if not more.

When the non-Chinese flight attendants would walk through the aisles during service, they would speak English to the passengers. And if the passengers didn’t quite understand, the flight attendants would just speak louder in English. But why should the passengers speak English? Why isn’t it reasonable to expect the flight attendants to speak Chinese?

On foreign carriers, we expect that the flight attendants can converse in English as well as the native tongue of the airline that they’re serving. And on some carriers like Emirates, it’s a badge of honor how many different languages are spoken by the crew. But on the American airlines that I’ve flown internationally, it seems like there’s only one or two crew members who speak the language of the destination, which seems rough for people who don’t speak English. And I don’t think it’s fair to expect the passengers to speak English, because I definitely don’t speak the languages of most of the places that I travel to, and I wouldn’t be able to order a drink or choose between chicken or beef in those languages either.

I guess it’s also not reasonable to expect that all crew members speak these languages either, but at least it’d be better if they didn’t get so exasperated when their passengers don’t quite understand English. And in general, speaking louder is not that helpful in trying to get someone to understand English.