Humans often only repeat patterns they've seen before as well, and quirky output comes from wild guesses and requires significant skilled labor to clean up.
For every new design you see, there may be 100 or 1000 that were thrown away. All of those discarded designs cost money regardless of if they were used or not.
Sure an algorithm can get the low hanging fruit that you say but what we really care about is computers competing with the best that can be made by humans.
I mean, it's going to be a long long time before we get an AI on the level of Iris van Herpen or Chalayan. It seems to be mostly about colour and minor variations on extremely basic articles of clothing, barely even "fashion" in the sense of innovation.
For every new design you see, there may be 100 or 1000 that were thrown away. All of those discarded designs cost money regardless of if they were used or not.