We’ve heard feedback that there are some instances where a post from a friend or a Page you are connected to is only interesting at a specific moment, for example when you are both watching the same sports game, or talking about the season premiere of a popular TV show. There are also times when a post that is a day or two old may not be relevant to you anymore. Our latest update to News Feed ranking looks at two new factors to determine if a story is more important in the moment than other types of updates.
Facebook hasn't explained why they made the change, but it could be in part a response to criticism of how little blue handled coverage of the Ferguson protests. Updates which mentioned the St Louis suburb were buried under virally popular content like ice bucket challenge videos.
To emphasize timeliness, the new algorithms place more weight on updates that correlate to trending topics on Facebook. When the topic stops trending those updates will drop to a lower position in your news feed or simply disappear altogether.
Facebook will also apply a similar filter to your personal updates; if it sees high engagement when the update is new, but fewer comments or likes later on, FB will assume your update's 15 minutes of fame has passed and will decrease its prominence.
I for one would prefer a simple chronological feed which only I could tweak, but we all know FB would never go for that. If FB didn't exert control then they couldn't charge for promoted posts or insert unasked for adverts.