Oh, this was done on purpose. The reason is because I noticed Lemmy only links cross-posts in certain cases, but not all cases. The cross-post text is just a good fallback in case Lemmy doesn't link the source post. For instance, I believe Lemmy only links cross-posts if the post has a link. For text posts, Lemmy will not generate a cross-post link.
I was also worried about cross-server support. Eg. if a post is shown in PieFed or something else cross-post linking can be broken.