Procedural generation can be far more complex than just linear blending, which is all that a shallow net can do. For example, consider the full generative process which creates a frame from the game No Man's Sky. It is enormously more complex than a simple shallow net that can just do linear blends of previous examples - many many nonlinear processing steps to go from a small random seed to intermediate databases for terrain and objects and finally down to pixels.

If you look at the actual net design used here, it's only a few layers deep, and not very big. Much much closer to 'linear blending' than what our brains do (which is presumably vaguely closer to what no man's sky does).