Because the population is letting them. These people DGAF about "Afghanistan" the nation in the western sense. The nation is not a nation. It's a series of t

Because the population is letting them. These people DGAF about "Afghanistan" the nation in the western sense. The nation is not a nation. It's a series of tribes, ethnicity and clans that happen to share an area that is all shaded one color on a map. Those groups are where their allegiances lie. They don't have a multi hundred year history of nationalism like European nations do. Furthermore lots of them don't really want a national government because national governments tend to try to steal power and control by these other institutions and homogenize things which they see as a negative.