Why does iCloud insist on storing thousands of Messages when I've deleted them on my devices?

Whenever I go to Settings > Apple Account > Messages on my Mac (or equivalent place on iOS) there is a dialog that looks like the attached. It says I have 60,000+ messages in iCloud. The thing is, I always delete my messages regularly from my two devices. They sync to each other right away and no messages are left in the display on a regular basis.

But for some reason, they remain in iCloud according to this dialog, and I have no way to purge it. Why would Apple think this is what I want our of this scenario? I DELETED THEM. I confirmed I wanted them deleted.

Additionally they're all still stored in my Mac's user library in a "Messages" folder at the tune of 8GB+ wasted. So basically I delete them in the interface but they're not REALLY deleted from my machine or iCloud? They're probably taking up space on my iPhone too. This is absurd, and also often results in very old messages showing back up on my devices.

And before you ask, no they don't take up paid iCloud storage space - that would be a separate issue and has nothing to do with my concern that they aren't deleting data when I request it so.