Teams, Sharepoint, Exchange, and OneDrive seem to be connected by a maze of dark twisty integration passages which no single human has mapped fully.

And every private channel as well. And if you rename the Team, the SharePoint will become out-of-sync and all URLs will still use the old Team name.

I knew I could smell a poo in the room, I didn't know what or who was responsible but it all makes sense now.