Ask HN: Why do threads die?

I'm wondering if anyone has an answer to my question. An example is currently on the news page:

http://news.ycombinator.com/item?id=1179711

I understand there are banned links, so those pages are automatically killed. However, I see this thread was killed without any reason- except for the author wrote the title and text without being very....proper?

Maybe we can start giving reasons (possibly) for closing threads?