Judges have made it through law school and typically are selected for their ability to make fair decisions according to the law. I lacked the willpower to survive a year of undergrad, but I have no trouble holding back my temper when others' wellbeing is on the line. It stands to reason that either I am a different kind of person than the rest of you, or that the average judge is better at this than me.

I don't know that judges are fundamentally power-seeking (I expect someone who has a judges credentials and wants power would rather be a prosecutor), but assuming so, I'm not sure I should expect someone who seeks power to be more beholden to their emotions than average.