Because they're positioned with higher status in a hierarchy?

If a student makes a mistake, the professor merely points out the mistake.

If a professor makes a mistake, a student will at least be uncertain whether a mistake was made, and will have to go to much greater length to point out the mistake.

A few templates, a couple of text expanders, and a brief mentoring in soft skills, active listening, and written comms would resolve any major issues.

Granted, Gaussian distribution guarantees that the above wouldn't cover all cases.