First off, why would you expect it to? It isn't as if the ability to create screw shaped water devices is genetic or something.

But, on a broader point, think of the three people you mentioned: Socrates, Galen, and Archimedes. Of those three, only Socrates was from Greece, Archimedes being from Syracuse and Galen from Pergamon. So one obvious answer to how the Greeks managed to accomplish so much is that the definition of "Greek" was very large.

Another reason is that during the late Archaic and classical the Greek city states were able to form a network of colonies spanning the entire Mediterranean basin. Their position gave Greece a far larger amount of wealth than would be expected otherwise, allowing for the development of a sophisticated urban civilization. Through conquest and assimilation they spread across the entire Mediterranean, such that Socrates is now a household name but his Tyrean equivalent is lost to history.

Modern Greece, on the other hand, has had a more troubled history. Wars and population movements in its first century of existence created a very unsteady political order. WWII didn't help, and civil war followed it rather than the recovery in much of Western Europe (fun bit: Greece received only about as much Marshall Plan funding as Norway). Despite that, there have been plenty of Greeks who have made brilliant contributions to the world--Spyridon Marinatos was one of the most prominent twentieth century archaeologists, Nikos Kazantzakis was an extremely well regarded author, Fotis Kafatos was the first president of the European Research Council.

Or to put it a different way, the reason Greece today is not in the same situation as it was two thousand years ago is that it isn't in the same situation