Should Iraq set the time table for us to leave?

What I don't understand is. Why don't we let their oil pay for our troops being their? Why should we bear the expense of the war? Let their oil pay for the repair of drainage and housing and schooling for their people. Why should the people of the United States bear the burden of this? I also don't understand why it takes the United States 13 weeks to train a U.S. troop and years to train an Iraq troop.