Loot is a big part of Afghan, particularly Pushtun (the tribe that produced the Taliban), culture. The things that are important to an Afghan include loyalty to family and clan, protecting the women, owning a gun and knowing how to use it, blood feuds and considering outsiders fair game for a little grand larceny, kidnapping or extortion. More than a few Afghans, watching Russian troops roll into the country during 1979, could only think, "look at all that loot."
This causes friction with many Pushtun tribes because they believe they are not getting their share of the loot (foreign aid) and that the non-Pushtun tribes (who comprise 60 percent of the population) are getting too much of that loot. While not a majority, the Pushtun have long been the largest minority in Afghanistan, and are accustomed to getting more than half of the loot.
Ah, the loot. Let us never lose sight of how important loot is in Afghan culture. Out in the hills, raiding other tribes, or foreign visitors, is considered great sport. Especially if you steal valuable, or neat, stuff. In the last century, a growing source of loot has been payments to the Afghan leader (formerly a Pushtun king, now a Pushtun president) by foreigners, to keep the Afghans from raiding outside their borders, or not providing sanctuary for Islamic terrorists. In other words, protection money. Which tribe got what piece of that bit of loot often led to the kind of tribal violence you now see in Afghanistan. And many of the Taliban factions are fighting over the issue of how much money, or other favors, they should get from the national government. Having the government leave the Taliban, and their drug gang buddies, alone, is a much sought after favor.
The culture of loot is more important in Afghanistan than most foreigners realize. Corruption is more visible to foreigners, but attempts to curb corruption always run afoul of the Afghan attitudes towards loot, and how enthusiastic Afghans are to get a piece of the action. Not just to be a little wealthier, but to have the respect and satisfaction that comes from taking loot from outsiders. This goes back thousands of years, and Afghan tribal legends still speak of ancient (and some quite recent) expeditions to the lowlands (Pakistan and northern India) to take vast quantities of loot. The current situation has brought heroic quantities of loot to the Afghans. No perilous travel required, just the ability to take your share, and maybe (for extra prestige) a little more.