Cannot merge first and second post in a topic even though both are written by the same author

What makes it special? Doesn’t this feature just merge the posts - in essence automating the process of copying and pasting the content and then deleting all but one post? At the moment, when a user (typically new) posts multiple times in a topic (because they can’t have more than 1 image), we merge all the posts (except the first) and then manually copy and paste the image links and delete the remaining post. Not merging with the first post removes a big use case for us from this feature.