Does Appeal Or Corporate Bias Explain Endorsement Gap Between Serena Williams And Maria Sharapova?

I don't really have an answer for the question posed in this title, but after researching some financial facts about player endorsements after Serena Williams won her 20th career singles Grand Slam in Paris on Saturday - defeating Lucie Safarova in 3-sets at the 2015 French Open - it made me think about the role which likability, beauty, corporate bias, and customer discrimination can potentially play in determining an athlete's value away from the sporting arena.