Forbes wrote an article with the title of 'How Gangnam Style Has Britney Spears (And Everyone Else) Dancing With Psy From Korea.'
The first reason was that Psy is born to be a star. He's not only funny but also charming and has a perfect sense of rhythm.
The second is that Gangnam Style has the catchiest dance ever with the horse riding dance. This dance, though it seems easy to imitate simply, is actually quite hard to perfect. Many have compared it to the Macarena, which took the world by storm years ago.
Thirdly, "Gangnam Style" appeals to all generations.
Lastly, because "Gangnam Style" is not in English, people are free to interpret it as they will. As a result, there are 3670 different parodies of the song and dance, which is fueling its popularity.