It’s probably girls making replicas of their favorite dance videos. Alternatively, one girl may have made a dance video for a popular song and other girls made videos of themselves after learning the dance. You can find American girls doing this, too. They stage their own version of a Britney Spears dance routine, or they create a routine for a video that doesn’t have one. Then other girls who like the dance learn it and post their own results. Sometimes it’s competitive, sometimes it’s just fun (girls who just want to dance or who really like inventing dance routines), and sometimes it’s just the human compulsion for mimicry. It’s nothing new. I had female friends who did this all the time back in the day. The internet just lets us share it with the world.