Everybody should timestamp all articles.

People don't want to because they want their content to be "evergreen" and they think that if there's a date that's more than a year or so old, people will disregard / discount the content. So by default many blog CMSs default to not showing the date of any articles.

Facebook is not a small blog operator. They should view this as a professional communications medium.

Someone in Facebook's PR department is reading this part of the thread and saying "it's working!"

If your content is "evergreen", show me a "last updated" timestamp in the last year.

/grump

published timestamps. another vestige of the earlier blog web.

You can thank SEO for that. Something about older content being less "relevant"

This is new, particularly the details around search history and location data being stolen, as of an hour ago.

I think it's the security incident that happened couple of weeks ago and they have more details now?

The first article has the date at the top: "October 12, 2018".

They might intend to repeatedly update the second one, which might be a reason not to put a published date on it.