Earlier quoted context omitted.
Are you sure visionOS requires it? Having an icon be a few px smaller so a microphone can stick out, doesn't seem like a big deal for tracking.
The thing sticking outside of the icon draws the eye to it, which means your focus is at the edge instead of the center, which makes for a more error prone experience. Since the eyes are the cursor, this is a problem. Desktop and mobile don’t have this issue.
And Apple decided this was a problem with icons, rather than a problem with the way they implemented their vision tracking? Believable, and laughable.