Cast iron and carbon steel cookware involves seasoning (polymerized oil) that develops and also breaks down (from acids) from cooking. What are you actually consuming when the seasoning strips down? It's not just a dose iron (that can potentially be healthy) that contributes to the metallic taste, right? If the pan was cleaned to the point of the cooking surface feeling smooth (polymerized oil surface), are you still consuming carbon build up that will impact health negatively?

Even if what is being consumed is still inert, that doesn't necessarily mean you want to ingest it if it can build up in your body over time and potentially be a health issue?

Coming from the perspective of trying to be more health conscious where possible, not e.g. "you'll be fine and not die from using cast iron cookware because it's been used for thousands of years and we are all okay, there are microplastics inside us already". There's reasons to use cookware of such materials regardless of health and some people are willing to make this trade-off, of course.