There are two important reasons to not disturb historical wrecks:
* In many cases the Baltic can do a better job of preservation than we can on the surface. It's survived 300 years down there, it's more likely to survive the next 300 if left in the same environment rather than introducing new effects. Put another way, anything that DOESN'T get preserved well in that environment is already gone anyway.
* It keeps the artifacts in their "context" - the place they were originally. You never know what new information may come to light later, and something seemingly insignifigant about the wreck site may prove to be important later. If you remove the wreck from the site, it's much much harder to link back all the artifacts to the place they came from.
* In many cases the Baltic can do a better job of preservation than we can on the surface. It's survived 300 years down there, it's more likely to survive the next 300 if left in the same environment rather than introducing new effects. Put another way, anything that DOESN'T get preserved well in that environment is already gone anyway.
* It keeps the artifacts in their "context" - the place they were originally. You never know what new information may come to light later, and something seemingly insignifigant about the wreck site may prove to be important later. If you remove the wreck from the site, it's much much harder to link back all the artifacts to the place they came from.