Currently, Instagram is not allowing people to post feed pictures to their stories because according to them, people prefer to see original photos and videos. This updated feature is a part of Instagram’s test to check the engagement of people. The test is being conducted in selective countries right now.
The following notification is being sent by Instagram to selective number of users.
The screenshot of the notification above shows that Instagram is stopping people from sharing feed posts in stories. They have also informed users about testing a change with respect to sharing to stories. This means users can not share normal feed posts to their stories. However, they can still share IGTVs and tweets regardless of this update.
This situation maybe annoying to many people but right now as a result of the testing change, Instagram wants to create a better user experience for people.