The reason old wood is valuable is because it has characteristics that are not available in lumber harvested today. These include grain, width of planks and density. Not because its moisture content has had several centuries to change.
These cycles bring out the best and worst of the wood. Obviously you are recovering old wood in a barn for other reasons as well, but in the ladder scenario, they want top notch wood that will last. Since SFFD has ladders that have been in active service since 1919, they obviously have that down.