Inherently everyone would know that rods exist on orbit and would destroy them before they reach an orbital position to deploy.

Unlike aiming conventional munitions, on-orbit maneuvering is extremely difficult and would be pretty easy to counter. Every nation that we would need that kind of yield from would be able to shoot the bus carrying the rod which would almost certainly disable the ability to accurately de-orbit it.

Basically, they are easily detectable and way easier to stop than any other weapon of mass destruction.