But we don't want to conquer Afghanistan. Our goal should be neither to rule Afghanistan ourselves, nor to install a friendly government, but simply to kill as many Taliban members and terrorists as possible, and smash as much stuff as possible, then leave the place to burn.
There is another way, of course. But it involves the use of hundreds of nuclear weapons and the death of millions of innocents, and I doubt few Americans would support it once they calm down a little.
As the article points out, the lower the level of infrastructure a country has, the less damage you can do to them with explosives. Basically, there is little left to blow up in Afghanistan.