How do I reduce iCloud size of my messages?

My messages are taking up about 5 GB of my iCloud, so I went into the top conversations and deleted a ton of videos and photos in my message conversations. Even though the number of GB in top conversations is down to about 1.5 GB, the amount of space messages are taking up in iCloud still says 5 GB, even after I've backed up my phone again.

I also have my messages synced to my Mac, and it seems as if photos/videos I delete from messages in my phone don't always delete from my Mac, and vice versa. I'm not sure if this is an issue with iCloud not being able to update, my messages app, or something else? I also cannot delete more than one picture or video at a time when I navigate to each individual message conversation > info > photos.