It's quite an organised crime. Taxpayers' money was going to the pockets of the Taliban in exchange for protection of far-off areas controlled by the militants. It is so formal that the Taliban even have an office in Kabul to negotiate the percentage they would get from foreign aid given to Afghanistan. Since most of these transactions occur at the contractor level, it's easy for them to skip the books. It is also crucial to understand that the little progress made over the course of two decades was contextual - possible only when the stability offered by the U.S and NATO troops was in place.