Picture book illustration uses a lot of the same elements as cartooning (both forms are Sequential Art) but it sure doesn’t feel like comics when you look at it and read it.
The visual continuity from image to image is tighter in the comics mode of storytelling, keeping the reader immersed in the world of the story while picture book illustration, even the most densely-detailed sort, keeps the reader at arm’s distance, each illustration acting as a visual anchor while the reader imagines the full scope of the scenario.
The two forms represent different aspects to imagination. Picture books encourage readers to visualize scenes based on the anchor points that have been provided. Comics encourage readers to explicitly empathize with the specific details as they unfold.