What Makes US Politicians Confused about the Afghanistan War?

Kabul Press^?: Still many U.S. politicians are confused why the most powerful world army could not defeat a terrorist group called the Taliban. In 2003, President George W. Bush used to say we bring democracy to Afghanistan and U.S. must spread democracy.
Now, after 13 years, the U.S. is sitting with the Taliban negotiating peace. Many U.S. politicians keep asking why a terrorist group forced them to do so, and why after killing tens of thousands of civilians and thousands of U.S. soldiers in the hands of the Taliban, the U.S. mission failed. Several former U.S. ambassadors have released a letter saying that “Equally strongly, we believe that US security and values, including support for women, require that a full troop withdrawal come only after a real peace. How our troop presence is managed will have a critical influence on the chances for successful peace negotiations, the future of the fight against the Islamic State, and the chance for Afghans to pursue representative government.”
To understand the complex war, U.S. politicians should look at the past, and do some background check finding the connection of Pashtun politicians such as Zalmay Khalilzad, Hamid Karzai, Ashraf Ghani Ahmadzai, Hanif Atmar, Omar Zakhilwal and Anwar ul-Haq Ahady to Pashtun nationalism and their policy to use Taliban as a military arm of Pashtunism. This will lead them also to the source of billions of dollars corruption paid from the tax of U.S. citizens.
In a country with several ethnic groups which is great supporters of democracy and liberal world, the U.S. could not identify the need for a federal system where power is not in the hand of only Pashtuns.
Any deal with the Taliban terrorist group and their supporters such as Ghani Ahmadzai force non-Pashtuns to seek support from U.S. competitors such as Russia and China.