They also have a lot of people who are not goat herders, and some cities and infrastructure that they would not want to see destroyed. The Americans had little trouble occupying Kabul, it was the countryside that gave endless trouble.
When you can get your act together and all be on the same side. But your country has at least two factions who increasingly hate each other. If a Republican leader wants to wage war, the Democrats will do their damnedest to sabotage it.
Not that the Democrats hate war - when in power, they just love sending young American lads to die in pointless, drawn-out conflicts with rules of engagement designed to get as many of them as possible killed or wounded.
When the US military starts helicoptering the people who've been actively trying to burn the place down from the inside, then the rest of the world will have reason to be terrified.