Rejection of illustration. Why?

Drawing errors here:

I think you need to do some research on techniques to increase the size of the picture. It just looks like a picture enlarged 2x in Photoshop.

The fish in the hand looks poorly pasted in after the fact, or a bad example of generative fill. I doubt that it's even need at all. Also, there is a tiny little spec of white on the female bear's cheek, and a little bit of fluff under her ribbon that I would personally have cleaned up before submitting. Both bears need a second eyebrow, and the one eye of the female bear could be a little more detailed.

The giraffe image is quite grainy when viewed at 100%. And while it's probably not a quality issue, I see no need for the hearts. They really aren't prominent enough to add much to the images.

on the first image I see artifacts where dark areas are near light areas. For instance around the noses. Also there are some rendering errors.