There doesn't seem to be a valid reason for it, but the native #macOS #NotesApp doesn't allow you to create nested #SmartFolders even inside non-smart folders. If you use tags and smart folders a lot, this makes organizing them in a way that maps to one's mental model annoyingly difficult.

#Apple should really fix this, as it's not a bug and shouldn't be hard to implement. Otherwise, someone should write an app for that. 🙂