Do downvoted answers disappear automatically? Or is someone removing them? I'm not sure that downvoted answers always disappear but I've seen them disappear on multiple occasions. Most recently, here.
I understand that it may seem cleaner to keep a question's page free of useless answers, but it's useful to have incorrect answers stay visible so that others don't go down that path again.
Also, useful comment threads can build on downvoted answers.