Yes, agreed.
But how does that affect the future performance of the troops?
Not trying to be argumentive, simply grasping for a root cause.
When the cause is a great one, men are inclined to be much more aggressive and more willing to take risks. Also, when you know you are going home after one year rather than at the end of the war, the primary goal is to simply survive that one year.
When you know the politicians and leadership at the Pentagon are unwilling to allow the military to invade and destroy the enemy, and win the war, why take unnecessary personal risks?