It is okay to miss out on something. If nobody crossposts it, it probably wasn't that interesting anyways.
If you are afraid that you are missing out on some content, then look at the crossposts in your followed communities. Maybe the communities that were the origin of the crossposts are interesting, and worth joining? Then you'll also see all their posts in the future.
If you want to see all posts that could remotely be relevant to you, you ultimately will have to follow all possibly relevant communities anyways. Because most users post their things simply to one community and call it done. And that's ok and good, and does not need changing.