Interesting point...but why would they degrade faster than regular lumber? (I ask not in a challenging manner, but out of ignorance).
Not an expert - but it has to do with the way the saltwater breaks down the molecular matrix of the wood.
Once the water element is removed (via drying out), it leaves molecular gaps in the structure that have for years been filled by water molecules. This results in a brittle, loose structure, that basically crumbles when touched.
Several other factors come into play, like the speed of the drying, etc. Which is why they often treat other old shipwrecks by keeping them in moisture for many years after they retrieve them.
Chemically treated wood will last much longer, because those ‘gaps’ have been pre-treated with chemicals that keep the moisture from wreaking havoc on the wood’s structure.
Waterlogged timbers that have been submerged for a long time typically have a case of rot that is arrested by the oxygen-excluding action of the water. Expose them to air, and they just crumble away,
A year ago, when the water got abnormally low, the wreck of a ferryboat was discovered in the Sulphur River here in East Texas. We decided our best course of action was to leave it submerged until such time as we have funds and facilities available to do proper conservation of it. Even so, underwater archaeologists who checked on it this year report that the parts that were out of the water (exposed to air) last year have essentially disappeared.
Some conservation techniques include soaking the timbers in glycol and waxes -- to displace the water, while simultaneously excluding air. That requires a big conservation lab and big tanks...
Watch for a FReepmail...