As the fight went on there was a lot of data that showed MANY of the fighters were coming from foreign lands. The primary motivation is as you have noted, the Americans occupying.
Most of my deployments were early on and the ROE, especially in the beginning, was very permissive as compared to later in the war. My first two deployments we were often cleared into a kill container and given free reign to shoot ANY vehicles. I can't tell you how many Toyotas we zapped, once we started shooting dudes with guns would pour out like a clown car. Interestingly, at least 50% of what I shot in that time period I found with my NVGs. Sensors are great but they are a soda straw. Using my NVGs I was able to scan large areas and would usually find a target within a few minutes. There were nights I went Winchester with a full combat load two hours into the Vul, landed at Bagram or Jalalabad, took another combat load and did it again. Gun over-heating limitations were a real thing. On my last two deployments I do recall the tight ROE, that being said, I never had a deployment where I did not shoot.
Impossible to know it would have changed the national debt. Remember we can't view the conflict with only a 2024 optic...In the days after 9/11 we were sure there would be more attacks unless we acted and we would be a vastly different country had we just taken that hit on the chin and turned away.
Beers, whiskey, coffee at my casa anytime for anyone that needs it.