I'm not sure that it has much to do with cravings. I also feed a homemade gel right now, and in the past I've fed Mazuri Aquatic Omnivore, OmegaOne pellets, frozen bloodworms... it doesn't seem to matter what I feed, they still demolish all edible plant life.
I think the major factor is whether or not the goldfish learned to eat plants early in life or not. For example, my goldfish didn't grow up with plants. So when I added them after they were adults, they immediately went to investigate (with their mouths) and discovered plants are delicious. But goldfish raised with plants seem to regard them as part of the environment and not food. This is just my own theory, I have only anecdotal evidence, but it's held true for me so far.