Actually, it was stated by Eiji Aonuma that the game takes place about 100 years after OoT. But yeah basically everyone just kinda seemed to not be concerned with the Triforce as much. And the people who are relatively new to the world in this game probably heard about the treasure and didn't...
The fish often refer to the Triforce as the "Golden Triumph Forks", because they don't exactly know its name. So the fish around Outset is talking basically about the Triforce pieces which are scattered throughout the ocean.