Why mass rocket artillery did not emerge in World War I

Why was there no large-scale rocket artillery in World War I despite suitable early rocket technology?

Existing artillery could be expanded more reliably, while industry lacked spare capacity to mass-produce and supply a new rocket system.

Demonstrating a weapon was much easier than producing reliable systems and ammunition by the thousand. Wartime economies were already struggling to meet shell demand, so scaling established artillery was easier than opening an entirely new production chain. Field armies could expand from familiar 18-pounders toward heavier 24- and 60-pounder weapons without creating a separate rocket industry. For still heavier or concentrated fire, they could call on naval guns or place naval weapons on railway mountings. The absence of mass rocket artillery therefore reflected industrial opportunity cost and supply-chain maturity more than a failure to imagine the launcher.