They got selected for deletion because of lack of community interest:

> If the question is more than 365 days old, and ...

> * has a score of 0, or a score of 1 in case of deleted owner
> * has no answers
> * is not locked
> * has view count <= the age of the question in days times 1.5
> * has 1 or 0 comments

> ... it will be automatically deleted.

(See [the original post on meta.SE](https://meta.stackexchange.com/questions/78048/enable-automatic-deletion-of-old-unanswered-zero-score-questions-after-a-year).) Deletions are done in batches, so it's not unusual to see a lot of them being deleted at the same time.

The easy way to prevent this is to upvote the question!