I like that dance. I did not know what it was or what its origins were when I watched it. Maybe she just likes and did the dance because it is a cool dance.
I think that people gravitate toward certain athletes because they reveal their personality. This is a part of Serena's celebrity persona. She transcends the sport, and people talk about her, and she makes more public appearances, and she makes money off of them. She is just selling a product, just like the Olympics is selling a product using her.