My guess is that this wasn't in international waters.
16th-Century Shipwreck Off Florida Coast Is Worth Millions. But It Belongs to France, not US.
A 16th-century shipwreck off the coast of Florida dates from the first French colonial voyages to the Americas – which means that the wreck's finders won't be allowed to salvage items from it, a U.S. judge has ruled.
www.livescience.com