Eg, if the tall green pill candy and the red round one both scale by exactly 3px when you drag them, it might still "look" wrong, and get into uncanney valley territory. And that's even assuming the LLM picked the same value to scale when you prompted it to "add a red candy", or it picked a different one arbitrarily.
I've tried making games a few times, or even CSS animations, and I can tell that they don't "feel" right, even if I have no idea why, or what to change. I have mad respect for artists and animators that can manage that, and I have no idea how you tell an LLM "It doesn't feel right when I drag the candies", and have it be able to figure out that a tall vertical candy needs to scale differently on the X and Y axis than a round one.
I am saying that a small subset of people care about this given what people choose to play in practice. It's currently much, much easier to not care about these things and focus on the cognitive aspects to capture player attention, and the human cognitive incentives are not stacked in favor of OPs view.