Can you elaborate on why?

I know both Python and Common Lisp, neither version looks any better than the other to me.

Also, as another commenter notes, the snippets are not actually good translations of each other. Your CL snippet would look like this in Python:

    list(map(str.tolower, ("Hello", "world!")))

While your Python snippet would look like this in CL (as pavelludiq notes):

    (loop for word in '("Hello" "world!") collect (string-downcase word))

Granted, Lisps tend to be a bit more verbose (longer names, less symbols used), which is a natural consequence of having little syntax. It has serious advantages when learning the language or when reading unfamiliar code, although it comes with some drawbacks, too.