In many ways, on release is even worse for shaky hands. Imagine trying to use the vote icon next to this comment with your hand shaking. You need to both click and release without leaving the icon, which is extremely small.

With on click, it only requires lining it up once before executing. There's less follow-through required. And as a best practice, there is an undo button.

Shaky hands or button manipulation issues can be a problem for act on release too. Click correctly but you aren't on target during release.