Why is it still not possible to cut files to paste them elsewhere in Catalina? I find it weird that this simple functionality doesn't exist in macOS, as it does in other OS. IIRC, it used to exist in the System 7 era.
What would be the rationale to get this simple functionality out of the window (I should say Apple here, I know ;) )?
Because the Pasteboard, to which all data is Cut, is inherently transient and unsafe. If you could Cut a document in the Finder, that document would only reside in the Pasteboard, and any new Copy/Cut action would cause it to be lost.
You could never Cut a file in Pre-OS X Mac operating systems.
However, you can achieve the same result by Copying (CMD+C), and then Moving (Option+CMD+V).