One possible reason is that the story might be copyrighted and you don't have the permission to share it. Another reason could be that it contains sensitive or private information that is not meant for public sharing. Also, there could be some technical glitches in the platform you are using that are preventing the sharing.
It could be that the story is copyrighted or has specific sharing limitations. Or perhaps the platform you're using has certain rules in place that are stopping you.
First, check the permissions. If it's a matter of lacking permission, try to get the appropriate authorization from the source. For example, if it's a copyrighted piece, see if there are any sharing licenses available.
Maybe it's because the person doesn't fit the plot or theme of the story. Sometimes, including them might make the story too complicated or take it in an unwanted direction.
There could be various reasons. It might be exclusive content or have specific usage terms that prohibit reposting. Sometimes, the owner simply doesn't want it shared elsewhere.