For example, the latter relies on more implicit information (the order of the arguments), which can be harder to keep in mind than the keywords use by the former, particularly as you add more than two attributes. I'd say this version actually reduces the cognitive load, but it doesn't save as many words:

    (sul
     (stylesheet :href "chrome://global/skin" :type "text/css")
     (window :id "findfile-window" :title "Find Files"
             (button :id "find-button" :label "Find")
             (button :id "cancel-button" :label "Cancel")))

Twice the disk space, who cares?

Twice the cognitive load, I guess I have a high tolerance.

Still don't see a compelling reason one is better than the other.