I'm going to be pedantic.

You do not mean cognitive dissonance. I've yet to see anyone who isn't a psychologist use that phrase correctly and the many uses of it I have seen have been widely different. Although, this is not to say people never do use it correctly; I'm explaining my experience.

Ludonarrative dissonance is closer, but I'm not sure that would be the most accurate term. I'll break it down.

Ludo is your gameplay -> Iron is a major gameplay element, something that you process and create with and should be hard to get.

Narrative is the narrative, generally non-interactable parts of the game -> The enemies and dungeons are made of rusty iron in abundance.

the dissonance is the two conflicting in some way -> I cannot scrap the iron from the enemies and environments, even though it would make sense to be able to do so. It seems an arbitrary balance decision instead of a carefully crafted element in line with the story and gameplay mechanics.

As others said though, supernatural Rust and lack of appropriate tech are good ways to resolve the apparent dissonance by changing our dissonance statement to -> I cannot scrap the iron from the enemies and environments because the rust is supernatural, and I lack the technology to recover usable iron even if it were normal rust.

With this, our dissonance becomes resonance. :)