See How can a post be deleted?
The post you linked to was flagged (for moderator attention), and was downvoted; but no-one had yet voted to close it (so it wasn't on track towards being deleted).
To delete a closed question, the system wants three high-reputation users (or one moderator) to vote to delete.
I reported this a few hours ago...
Flags are only seen by the moderators of this site (they're not seen by all 400+ SE moderators), and that can only happens when a moderator is awake and reading the site. That tends to happen every day but not every hour, so don't be alarmed if something flagged takes many hours to be processed.
Taking fairly immediate action might be one of the reasons why SE would like the community to act instead of only depending on moderators.