The modern Olympics are just that - modern. They were proposed at the end of the nineteenth century by Pierre de Coubertin, a French aristocrat who believed passionately in the physical and spiritual benefits of athletics, and sought to create a global athletic competition that would showcase those benefits and foster international cooperation. To Coubertin, the ancient Olympics - last held nearly a millennium and a half before - seemed an ideal model for his new games.

As you note, the Olympics were one of the four great games that dominated Greek athletics. Even in the Roman imperial era, when there were literally hundreds of regular athletic contests, the great athletes who earned their living from prize money always treasured the wreaths they earned in original four Panhellenic games above all else. Of those games, the Olympics were always foremost.

They were foremost, in large part, because they were first. According to the reckoning of later Greek historians, the first Olympics were held in 776 BC. We don't know when the actual first games were held - they probably developed gradually from a local festival over the course of the eighth century BC - but it is clear that they were the first games to attract athletes from every corner of the Greek world. The other three Panhellenic games developed later, and after the example of the already famous games at Olympia.

The answer to your question, in other words, is straightforward: you've heard of the Olympics because it was the ancient Olympics - always the most famous Greek athletic competition - that the founders of the modern games chose as their model.

The Olympics didn't "go the distance" in all those centuries between antiquity and the nineteenth century. They were last held sometime in the fifth century (contrary to what is sometimes said, they seem to have survived the ban on pagan festivals issued by Emperor Theodosius in 393), and endured through the Middle Ages only in the testimony of classical texts.

The Olympics re-founded by Coubertin & co. in 1896 actually had relatively little in common with the ancient Olympics. Although they kept some of the ancient events - sprints, wrestling, discus, long jump - they discarded others, such as pankration (a brutal and virtually rule-free combination of wrestling and boxing) and the armored sprint (an event that involved nude runners with helmets and shields). The events of the 1896 Olympics were really meant to showcase a modern (western) athletic tradition only tenuously connected with its classical roots. The Olympic torch, the marathon, and many other ancient-seeming elements of the modern games were inspired by other classical antecedents or invented wholesale. Like so much else in western (and now global) culture, in short, our Olympics are a distinctively modern appropriation or reinvention of the classical reality.

If you'd like to read more, you can check out this fun page on the official website of the Olympic Games, or this page run by the University of Leuven. My favorite book on the topic (which includes an interesting chapter on the origins of the modern games) is M. I. Finley & H. W. Pleket's The Olympic Games: The First Thousand Years.

In the meantime, of course, I'll be happy to answer any and all follow-up questions.