There are a few reasons. It could be a technical issue with Instagram itself. Or, your friend might have chosen to only share their story with a specific group of people and you're not in that group.
It could be that your friend's account settings have changed, or there could be a glitch in the app. Sometimes, if your friend has a private account and has removed you from the allowed viewers list, you won't be able to see their story.
Maybe they've blocked you from seeing their stories. Another reason could be that your app needs an update. Sometimes, glitches in the app can also prevent you from seeing stories.
It could be that you were unfollowed by that person or they blocked you from seeing their stories. Another possibility is a glitch in the Instagram app.
Maybe your friend has restricted sharing or your Instagram app is having glitches. Check your settings and update the app to see if that helps.
Maybe your friend has set their story to private and only allowed specific people to view it.
Maybe your friend has set the privacy settings so that only certain people can view it.
Maybe your friend has set some privacy settings that prevent you from viewing it.
Maybe your friend's account has some technical issues or restrictions preventing them from reposting.
Maybe it's a glitch in the app. Sometimes Instagram has technical issues that prevent this feature from working properly.
There could be a few reasons. It might be that the people who viewed your story have chosen to remain anonymous, or it could be a technical problem with the platform. You might want to try logging out and back in to see if that fixes it.
Sometimes, it might be because the people who viewed your story have chosen to keep their viewing activity private. Or, it could be a technical issue on Instagram's end that they'll fix in an update.