Facebook giveth and Facebook taketh away. App startups have known this for a long time; now The Washington Post and other news publishers are learning the same lesson as Facebook makes it harder for articles to go viral.

Facebook’s manager of media partnerships was quoted at a journalism conference saying the social network is moving away from so-called “passive sharing,” in which reader apps from the likes of the Post and The Wall Street Journal are able to broadcast activity without any prompting.

Indeed, some changes have clearly been made already. As BuzzFeed noticed, it’s been getting harder and harder for news-app activity to get past Facebook’s software algorithms and into people’s news feeds. Below right is a look at how Facebook’s changes cut the Post’s app traffic nearly in half in just one month (via BuzzFeed).

's Social Reader app on Facebook. AppData via BuzzFeed

This is a phenomenon you might call “Facebook whiplash:” Apps like the Post’s social reader get a big surge of traffic as Facebook opens its platform to a new category, only to fall back to Earth after Facebook users complain and Facebook cuts activity from that category out of users’ news feeds.

Something similar happened to Zynga, which built a multibillion-dollar business making casual games that spread virally through Facebook’s news feed. Then Facebook made it harder for gaming activity to show up in the news feed, and Zynga cratered. Below right is a chart showing what happened (via Business Insider). It looks a lot like the chart of the Post app above:

Daily Active Users of Zynga's games on Facebook. AppData via Business Insider

A similar algorithmic change has been blamed for the quick rise and sudden fall of video-sharing apps on Facebook, although in that instance mischief-making on the part of app makers may have forced Facebook’s hand.

In the case of social readers like the Post’s, Facebook says it is simply incorporating lessons it has learned about what kind of experience its users want. Specifically, they want more control over sharing, which is why Facebook just rolled out a new set of controls letting users more easily block third parties from broadcasting user activity on Facebook.

Facebook doesn’t want random companies making fast money by aggressively sharing user data in the manner of Zynga, SocialCam, and the Post's reader app. After all, if anyone’s going to do that sort of thing, it should be Facebook.