Because the UCMJ prohibits it.
Once you have active duty military officers publicly challenging the civilian leadership, you have crossed the Rubicon as Caesar did.
If there are problems, they need to be considered in a dispassionate manner without a knee-jerk defense of any particular individual. American military history is replete with both know-it-all Generals (McClellan, Hooker) and civilian micro-managers (McNamara, LBJ) that brought disaster to U.S. war efforts.
This is an issue where the debate should focus on military specifics and not on personalities.
One issue I agree with is the the Bush Administration has done an abysmal job in regards to fighting the Home Front Propaganda War........Not only in Iraq but even with domestic issues such as Katrina.
Say what you will about Bill Clinton, he was a master at molding public opinion. Even though Clinton had the liberal news media firmly in his corner, Clinton's "War Room" would mount a frontal attack on any public relations problem within one news cycle.
By comparison, when the Democrat Governor of Louisiana and the Democrat Mayor of New Orleans ignore their own evacuation plan and leave tens of thousands of poor people stranded in a flood surge zone, the message that America gets is, "Bush hates black people" and the reply from the White House is:
