They are not silent. French doesn't work like English, where you mindlessly pronounce the letters after each other in a string. French letters function by groups, by phonemes.

You try to mock "eaux," but it actually illustrates my point. In English, you would read it "E" then "A" then "U" then "X," making an ee-aaa-ooo-xxxth sound. In French, you don't. "Eaux" is an established phoneme that will always be pronounced the same, it's not like one part of the word is just skipped over, like English does sometimes. It's not silent letters, it's English speakers who know nothing of French grammar wrongly assuming that both languages work the same way. A "E" at the end of a French word is not pronounced on its own, because French grammar establishes very clearly the roles of "E" in a word; it is not a letter that is here for no reason, it actually does something. And it is actually pronounced if you know French - when a word ends with a "E," there is no liaison with the next word, while a liaison would be used without the "E," clearly denoting its presence.

TL;DR: Uneducated Americans point and laugh at something they don't know, because they assume their failure to understand it means it is absurd.

Copy pasting my own explanation.