Obviously because then any head of government would have had personal experience with military service and if they survived and did not die in battle and became head of the government they would know what waging war was like for those on the ground who fight and die. As it heads move military around like chess pieces. Detached indifferent uninvolved uncaring. Mebbe they should be experienced. Wouldn't that be by far the BEST?
What would be so bad about that?