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.) 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!
