Facebook does fact checking because people decided to blame them for misinformation rather than the people actually doing it. Their customers demanded that they take action, so whether or not the action is useful, they were required to do so.
Which should be pointed out isn't the same as Facebook's users. Facebook's customers are powerful entities that already have nearly unlimited access to promote their messages. What upset them was the ability of others to also push messages, some of which were inconvenient to the powerful. What Facebook's customers are demanding is that only messages they approve be heard.
The algorithmic news feed incentivizes misinformation in a way that the old chronological feed did not. Facebook absolutely helped to create this situation in the first place.
