Insouciant

This isn’t a big deal, but it is something that I have been wondering about. There are two French words that we use rather frequently in English: “insouciant” and “nonchalant.” It occurred to me that these words mean roughly the same thing. So I looked them up, and sure enough “nonchalant” is given as a synonym of “insouciant.” So my question is, why do the French have two words for an attitude that English-speaking people have not come up with a single word for? I guess “carefree” is kind of close in meaning, but not exactly. Please respond with any thoughts you might have.