Hmm but then is the scope/namespace reserved for each user that reserves/uses it? If I publish @andy9775/left-pad can someone publish under @andy9775/other-module or can only I publish under @andy9775/...?

If so, why is no one using this???

Yes, namespaces are specific to your username. Nobody else can publish packages under your username namespace.

I think it's less common because it was released along with private modules and is often conflated with them. Basically all packages are still namespace-less. TBH I never thought about the benefit they'd have until now.