Actually, in similar situations of organized harassment of someone by parts of your community, streamers often act on Twitch.Worse still, yo/lyx didn’t attack vivi, but neither can they do much when some of their fans just go berserk in fatdragon’s chat…
I've seen numerous interventions of the type of "whoever does that is not a part of my community, and you're not welcome on my stream", and some went further and banned the toxic minority of their viewers for what they said on other chats, even if they were "clean" in their own chat.
Immediate actions are also very important to give the right example to your viewers and avoid starting a cycle of harassment.
It seems we're right in a cultural difference between Douyu and Twitch. I've had several echoes that moderation on Douyu worked really differently and that big streamers there had usually less rules than Twitch' big streamers. Some people in this thread can probably give us more insights on how moderation works on big Chinese streams.