That's a huge amount to just walk away... and what isn't pointed out is what this does.
Almost certainly, those who left were predominantly Arab, who don't want to fight their own. This means that the bulk of the Iraqi army will be associated with the Kurds... and the thought of armed Kurds going to other parts of Iraq and potentially killing people there is likely to create bigger factional rifts in Iraq, as well as discrediting the validity of the Iraqi army. The Iraqis won't view it as the people's army, but as an extention of the occupying force.
Also of note is that there are reports that the resistance have infiltrated the army. In other words, we're paying to train and arm Iraqi army forces who promptly leave the military, only to attack our soldiers. Some of these potential resistance fighters get discovered and have been quietly mustered out, but most of them appear to stay in until they get their training. This would also explain beligerent statements from members of the resistance that if the army or police moved against them, they'd be given immediate notification before they even left.
As a result, much of Iraq is locked in a state of increasing paranoia. Westerners can be kidnapped by almost anyone, who can, in turn, sell them to the headcutters. Iraqis aren't safe from the kidnappings either, with the savings of an entire extended family being depleted to free relatives... and Iraqi police are reported as just driving on by if they see a kidnapped Westerner. Go along to get along.