Over the years, some words are shortened or meanings change. Look at the word "awful", which originally meant "full of awe". That's why a sentence like "That's an awfully pretty sunset" still coexists with it's other meaning of "That was terrible".
I've heard that 'butterfly' was originally 'flutterby' (which makes more sense), but got changed over time by the majority enjoying to flip it around for fun. Don't know if that's true.
The English language does get wacky.
Why do we park in the driveway & drive on the parkway?