The United States has a military, intelligence, and moral reason for American forces to remain in Afghanistan.
The Taliban fighting the Afghan government is a declared enemy of the United States. Leaving Afghanistan ensures that the Taliban will take over most of Afghanistan, which sadly is happening at a quickening pace. A Taliban victory opens Afghanistan to be a hotbed of terrorism as it was after the withdrawal of the Soviet Union and the United States and before the events of September 11, 2001.
Secondly, American withdrawal from Afghanistan creates an intelligence vacuum. American ground forces and their intelligence allies were great surveyors of information operations on the Taliban and international terrorism in Afghanistan. Further, such intelligence gathering extends to other interested parties in the area such as the Chinese, Iranians, Russians, Pakistanis, and other Central Asian nations. It is unconscionable that in one of the areas that can truly be described as a crossroads of the world, the United States will have little to no intelligence gathering capability. This lack of intelligence gathering capability will have profound implications regarding assessing capabilities of enemies of the United States, whether conventional or unconventional, as well as ascertaining future threats.