About the wood: I don’t know why some wood rots, and some doesn’t. And I don’t know the temps of the waters where the ship sank. But, they have recovered loads of wood lost in the Great Lakes from the late 1700s to the late 1800s and they sell it for furniture. It’s quite valuable.
I think the wood you speak of is at extremely great depths and sometimes protected by the mud at the bottom.
Very interesting comments about the wood. As a young man, I did a bunch of salvage and relic diving around the Channel Islands in Southern California. We recovered many artifacts around old wooden hulls that had been down for well over a century. Much of the wood was still in tact. It is just difficult to say what effects what types of woods. The water temps ranged from about 55-70 F depending on the time of year mainly and depth.