Have to use infantry for that. And if they did that, well, eh, have to worry about the villagers attacking them or just casualties in general. Not good PR for them to drag US bodies around the street chanting, etc., heh.
Drone strikes or air strikes are a lot more low risk, hard to make something like a guided grenade in terms of explosive power, therein lie the problem, as you vape everyone nearby with a Hellfire (overkill to use an ATGM for a man, really). But even doing that - sending troops in to kill the target- at this point is not going to deter the "it's a war on Islam" jihadists, so they'll keep plotting and keep doing stuff like this.