I don’t think this is categorically true. A couple obvious options are constructing titanium gliders to land materials on earth, and de-orbiting incoming metal loads with a space tether to provide inertia that can then be used to launch planetary loads to orbit.

It’s true that the relative value of these materials will be higher in space (since your alternative is lifting it out of the gravity well) but there may be so much supply that you can saturate the space market and justify the extra transport cost to sell it on earth too.