|Greetings from the Critique Club
I think the choice of subject was perfect for this challenge and I love the choice to use black and white. I suspect it is a bit disappointing to get a low score for this, as it does meet the challenge topic pretty well.
Sadly, I think some technical issues are letting you down with this image.
Composition: Nothing really wrong with the composition, but it's possible that it could benefit from having a little bit more of the background surrounding the subject. The bottom edge, the cauliflower is very close to the edge of the frame.
Exposure: To my eye (and when checking the histogram) the image feels a little bit underexposed. I think a very minor adjustment to levels or curves would bring some life into the image and yet still retain the low key look that was clearly what you were aiming for.
Focus: This is one of those images where the focus needs to be spot on. In this image the focus really is a little bit off. you make no mention of using a tripod or another form of stabilisation. 1/8 of a second is a bit on the slow side to get a sharp image.
It's such a pity about the focus, for I'm certain if this image was sharp, it would have scored at least 1 full point higher than it did.
I noticed you have joined DPC quite recently, so don't let this one put you off. Keep entering and welcome to DPC.