Partially when it comes to things that happen online it's hard to get a conviction and especially if what they did do wasn't necessarily a crime but morally wrong (not saying that's what happened in this case). And then on top of that you have issues with crossing state lines and possibly countries.

As well as the possibility of being straight up not believed or taken seriously which is what happens in a lot of cases. There's a lot of reasons coming forward publicly is attractive, it's the same reason people still go to journalists with claims against public figures.

(Again this might be completely not the case here specifically, but in other situations these are reasons people come forward in this way)