You have custom access

Select your Home folder, or any of the standard folders inside it like Documents, and Get Info. In the lowest of the sections, Sharing & Permissions, does it report that “You have custom access”? Do you know what that means?

Custom access is Apple’s jargon to let you know that macOS has set an Access Control List (ACL), in this case to prevent anyone from deleting those folders. If you’re good with Terminal, you can use the command ls -led ~

there to see the details that the Finder is too coy to reveal. But oddly Apple doesn’t explain any of this. If you’ve invested in a utility like TinkerTool System (bresink.com), you can view and change ACLs with ease. While they can get you into trouble if you’re not careful, it’s frustrating that Apple uses them but doesn’t trust us to know about them.