This article says long tradition of tribal deals lead to the quick surrender of Afghan forces

[mrsadm]

I found this an interesting opinion, from a former London Times journalist:

"In the winter of 1989, as a journalist for the Times of London, I accompanied a group of mujahedeen fighters in Afghanistan’s Ghazni province. At one point, a fortified military post became visible on the other side of a valley. As we got closer, the flag flying above it also became visible — the flag of the Afghan Communist state, which the mujahedeen were fighting to overthrow.

“Isn’t that a government post?” I asked my interpreter. “Yes,” he replied. “Can’t they see us?” I asked. “Yes,” he replied. “Shouldn’t we hide?” I squeaked. “No, no, don’t worry,” he replied reassuringly. “We have an arrangement.”"
[link:https://www.politico.com/news/magazine/2021/08/16/afghanistan-history-taliban-collapse-504977|]

[JoanofArgh]

1. He's probably right.

[sarisataka]

2. Something no US administration

Has been able to comprehend when dealing with most Middle Eastern countries. We tend to believe the government or a well organized opposition movement is the power broker. We don't understand that there is a cultural norm that is the true power. It is more difficult to manage as it is decentralized but if you can make a bargain the National government will have no choice but to accept it.

[Phoenix61]

3. I don't know much about the geography of Afghanistan

but in areas of food or water scarcity it makes sense to find a way to settle disagreements quickly and with little loss of life. This prevents the victors from dying from lack of food or water along with the losers.

[Klaralven]

4. The power of kinship...

The power of kinship led to a common arrangement whereby extended families have protected themselves by sending one son to fight with the government army or police (for pay) and another son to fight with the Taliban. This has been a strategy in many civil wars, for example, among English noble families in the 15th-century Wars of the Roses. It means that at a given point, one of the sons can desert and return home without fearing persecution by the winning side.

These arrangements also serve practical purposes. It is often not possible for guerrilla forces to hold any significant number of prisoners of war. Small numbers might be held for ransom, but most ordinary soldiers are let go, enlisted in the guerrillas’ own ranks or killed.

In war, the objectives are to survive and to be on the winning side.