How come with all of the shipwrecks that are in the Mediterranian Sea , they are just starting to investigate?

Often, the shipwrecks are so overgrown with sea-life that it's difficult to tell whether it's actually a ship, or a natural formation.

The Mediterranean is approximately 1,000,000 square miles, a Greek trireme is estimated at around 40 yards long and 6 yards wide. Made of softwood there is very little of the actual ships left except for the metal fittings.

Your premise is invalid. The Mediterranean is one of the most heavily investigated and surveyed bodies of water in the world. But many of these wrecks are in much deeper water than someplace like the Caribbean, and the level of technology is only now allowing for close exploration of those depths.

Wrecks in the Mediterranean have been explored for centuries.

Ahhh, the ubiquitous they. Who are they? Are we they? Are they we? Could we be we and they be they? They say, who says? Who says they say?