The phonology of “moth” is just bad (not just subjectively but in a way that I’m sure linguists could pick apart). It’s adjacent to “moist”. That’s the kind of name you give something you don’t like, a name made to be spat out. Contrast to other monosyllabic names like “fly”, a decidedly more despicable insect but with a much prettier name. Which one would be easier to use in a song?

Also I just checked and moths are butterflies, etymologically it’s just that old Germanic peoples assigned a different name to the less colorful butterflies.