It wouldn't take more than one brief comment from the athlete.
Look at the awful (and scary) things some of the Yuna fans said about Adelina after Sochi. Literal death threats. Yuna was so revered, I believe that just one comment to fans would have curbed all of that. I have to admit that my respect for Yuna faded somewhat, because it almost looked like she was okay with all of the threats and nastiness against Adelina. (Not saying that was the case, I have no way of knowing what she thought.)
Well then people would expect her to say something about her fans harassment to Asada all those years, and then it becomes why didn't Kim speak out on this issue or that? Then people start making character judgments based on when she speaks out and when she doesn't. It's a slippery slope and superstars would benefit from not going near that slope.
Beyonce has a rabid fan base and there's never an expectation that she speaks out to moderate the Beyhives action. Shes not spoken out even when her fans go on harassment rampages.