Moving is expensive and time-consuming. Moving out of a war zone is worse. StrategyPage details our costly exit from Afghanistan:
Serious planning for the withdrawal began in 2011 and ended up costing nearly $30 billion. The United States had the biggest job because they had most of the bases (500), vehicles (nearly 25,000) and shipping containers (over 60,000) to deal with. Many of the bases were turned over to the Afghans although facilities the Afghans could not use had to be destroyed, especially bases, lest the Taliban or drug gangs take them over. Some heavy equipment that the Afghans did not need (or could not use), like the older MRAPs, were destroyed (disassembled) in Afghanistan.
Originally the plan was to move 60 percent of the cargo containers out via roads through Pakistan to the port of Karachi where it would move by sea back to the United States and other NATO countries. That proved more difficult than expected because Afghans and Pakistanis saw this as a splendid opportunity to make money. Rather than pay more bribes to get the trucks to Karachi, a lot more of the stuff was moved out via air freight. Some was flown to the Persian Gulf where it was transferred to ships for the long voyage home. That was more expensive than paying more bribes but was seen as a better way to go as the cash goes to Western air freight companies and not some tribal outlaws.
Moving is said to be the third most stressful event a person can go through, just behind losing a loved one, and divorce — which amount to nearly the same thing.
Now multiply that by thousands of soldiers and billions of dollars and untold tons of equipment.