One reason is devotion to the rule of law. Another is you get to boss people around. And given that "qualified immunity" is still a thing, most serious mistakes

One reason is devotion to the rule of law. Another is you get to boss people around. And given that "qualified immunity" is still a thing, most serious mistakes - or even outright criminal actions - go unpunished or punished by administrative means like demotions or firing - a luxury that a common citizen is never allowed. Hopefully, the majority is in the former category - but let's not close our eyes to the fact the latter category exists too.