Several things make it difficult to search for treasures in the seas. This is in spite of the fact that the seas are known to be full of all sorts of treasures: including gold shipments that sunk centuries ago to oil deposits, mineral and sorts of other valuable things.
The first thing that makes it difficult to search for treasures in the seas is the vastness of the sea. The sea is a very vast place, and getting the exact locations where the treasures are can be a very daunting undertaking indeed. You just need to have followed the stories in channels like the CNN and Aljazeera about the search for the lost Malaysian Flight 370, to understand just how vast the sea is.
The second thing that makes it difficult to search for treasures in the seas is the whole range of hazards associated with that sort of undertaking. Simply put, the task of looking for treasures in the seas is not a task for the faint-hearted. There are so many things that can possibly go wrong: from getting caught in sea storms to pirates (who, by the way, are still in operation in certain parts of the world) and everything in between.
The third thing that makes it difficult to search for treasures in the seas is the cost of doing so. This is perhaps as a consequence of the vastness of the sea that we talked about earlier. Sometimes, one just looks at the sort of investment they have to make in search of treasures in the seas, against the sort of return they expect to get, and they opt to simply forego the search.