I get your point.
However, not everyone follows the official preparation instructions. With time, each person may find its own preparation method . 5 people so far have participated in The Perfect Preparation Method and there are already 4 different preparation methods. Making all of the markers visible would probably be aesthetically unpleasant.
I usually put my finger on the desired marker while pouring water, although by now I almost know when to stop by heart. The limit that I use for the powder is none of the volume markers, actually, but the visible bottom circumference where the top gets attached.