My kitchen scale won’t measure below one gram, and a lot of things (spices and flavorings, mostly) are used in amounts below one gram.
So I can either dirty up some spoons, or go buy a second scale that only gets used for the small stuff…
In general I agree, of course, but there definitely is a use case for volumetric measuring spoons.
The US and Russia are not bound by that treaty (according to a quick search), but they should be.