I didn't see this question until earlier. That's why the site guidelines ask you to email hn@ycombinator.com if you want to ask us something: https://news.ycombinator.com/newsguidelines.html

We turned it on temporarily because HN was under attack by an account-stealing botnet. Obviously we don't leave it on any longer than we have to. We also are happy to put anyone's username on a whitelist, as the people who emailed us found out.