The commercial exploration of the shelves is in some ways more sophisticated, but not tailored to find this kind of stuff.
I presume you're referring primarily to oil and gas. Are you aware of any systematic effort to search for other "stuff" on say, OUR continental shelves? Seems odd to me that various governments, NGO's and even individuals are willing to drop some fairly large bucks looking for everything EXCEPT signs of old civilizations just offshore. Most such finds have been accidental discoveries made by fishing trawlers and the like. There almost HAS to be more down there so why isn't somebody looking for it? Or if they are, why don't I know about it??? ;^)