I guess the logic behind those rules is to maximise the chance for negotiations to be successful. If both countries are in chaos because their leaders keep getting killed, who are you going to negotiate a cease fire with?
Of course, this is assuming all other rules (only targeting military infrastructure, minimising civilian casualties, etc) are followed, which pretty much never happens.
I do agree with your point that the elites are way too isolated from the consequences of war, which makes them way too hawkish for their own good.