The book author Sarah Chayes argues that corruption leads to insurgencies or at least normal civilians turning a blind eye to them, why help the government/police when they've been grafting all over the place.

To me it's also clear why the Afghani army gave up, (if it even existed, it's probably like the ghost schools and students): a leader that was (or appeared) clean and inspirational might've been able to generate a sense of national pride, which the soldiers would've fought and died for. But the soldiers probably knew the elites were corrupt scumbags, who wants to die for that? (Unless the embezzled riches tricked down to them...).

Edit: reading your article makes me think of "reality must take precedence over public relations". It's disgusting to see how the US institutions deluded their way into reporting success, it's almost comparable to the legend that said Saddam Hussein probably thought he had a great WMD program, because all his subordinates were too afraid to bring him bad news..