From Facebook they are working so that the stories shared on that social network can also be shared on Instagram. Currently it only works one way: Instagram stories can be shared on Facebook.
This new dynamic will allow users who publish the same content on both networks, to do it in a simpler way just by modifying the privacy controls, checking to share history on Instagram.
From the point of view of the company, beyond knowing that Facebook and Instagram have different audiences, this strategy collaborates taking traffic from one network to another; and brands favor them by adding authenticity by showing themselves in the same way on both networks.
Facebook ensures that cross stories is just one of the functionalities in which it works in order to improve the user experience, the main element for the success of these networks.