Because they are designed to look good for us on television. This was how they wanted to fix the image problem they had during Viet Nam. They showed us videos of smart bombs walking right in the door, shaking hands, and exploding. Of course, years later we found out they didn't always go to the right house, or office , or factory.
Smart bombs might be smart for neocons who are so cynical that they believe Americans will accept a gizmo war that delivers for us an acceptable level of civilian casualties. We do accept this, of course. Some people think it's neat.
Read A History of Bombing and that whole "it's just a little precision high-tech bombing" security blanket that lets you continue to believe that our leaders are always thinking everything through, that they're always thinking of the big picture, and that they've got a plan, and that those smart bombs make the people we bomb in order to liberate somehow hate us less- that security of conscience evaporates.
Americans Acknowledge Hitting Wrong Target in Iraqi Airstrike, Killing at Least Five; Iraqi Says 14 Killed Oh well, you gotta break a few eggs, right?
Thank you, Micah Ian Wright