[Retric]

There is a wide range of comfortable shapes people can make using whole hand motions, but arms have a vastly more momentum than the tip of a pen. So for example the center of an uppercase E is much harder to do using whole hand motions if you need to stop your arm motion in the middle to add details. It can be a fairly direct tradeoff between legibility and readability. Scripts that are less legible because they lack detail can quite simply be far easier to pull off.