See attached picture of my cauliflower plant in my raised bed. Other plants are healthy but this one does not look as healthy. What could be the reason?
It looks as though it's been ravaged by insects. Are you sure you don't have cabbage worms, aphids etc attacking this plant.
Sometimes I see that the weakest plant in a group of plants gets attacked by insects leaving the more healthy ones alone. That is it becomes the honey pot limiting damage to the other plants.