It really boils down to the species and the conditions. You are only able to cover a limited area and shallow depth and limited amount of time as a diver. Many species of shark are likely to know you are there before you know they are there and sharks can be shy and avoid divers. However certain shark spots can be popular feeding grounds, sleeping grounds, or mating areas. While I think there is a lot more historical pressure from fishing sharks in the Mediterranean, I don’t think there is anything innate about the sea there that makes all shark species there shy. I have heard of shark spots in Lebanon: http://www.nisd-online.com/article-101506-talesanddivesinlebanon.htm, though I do know the Red Sea offers a lot more in terms of shark encounters. There simply is a lot that goes into a shark encounter and we do not know nearly as much as we would like on their behavior. I’ve been on many dives in different parts of the world to see hammerheads in the wild and it can be a shot in the dark. It takes many years of local knowledge of the species’s behavior and conditions (season, tides, current, temperature, time of day, moon phases, undersea typography, etc). They are out there, but my best advice is to speak to fisherman and local divers, and also get creative in how you approach them (think about boat sounds, consider beach entries only, go in small groups, try early morning, try different seasons, etc.) Many scientists doing research on certain species in a locale find talking to fisherman to be a huge source of knowledge too.