It wouldn’t physically work using cheaper wood, or if there was any play at all in the joints, because the structure only has stiffness in two planes. If you made it from pine, even with perfect joints, it would slump sideways and the joints would probably explode like one of those hydraulic press videos from all the torque.
For real-life shelves, you need a third plane of support in the form of a back board, fixing to a wall, or just a diagonal strap (you can see what a difference it makes when you assemble Ikea Ivar shelves, which flop around like a jellyfish until you add one flimsy metal brace and they become magically rigid)
