Because "Worse is Better" entered the lexicon circa 1991.
In Gabriel's opinion, Unix proved to follow the more adaptive design strategy in certain ways (in spite of his involvement with and admiration for Lisp), and the phrase "Worse is better" is meant to capture the essence of that advantageous strategy (as outlined in the essay).
The essay is worth reading and is a bit more elaborate than just saying "less is more", or "keep it simple, stupid".
yes, this is a much better explanation than the wikipedia