The answer is airplane doors. An airplane door is not a simple metal flap. It is a highly pressurized, safety critical aerostructure requiring agonizing multi year certifications. Aerospace titans cannot 3D print a replacement. They cannot easily pivot to a new vendor. Absolute market power shifts to an unexpected place. Airbus is a European titan. Deeply rooted in French and German engineering pedigree. Historically backed by billions in regional government subsidies.