A) The US built the Afghan army and state so that it would be utterly dependent on US support, and later withdrew in such a way as to maximize Taliban advantage

A) The US built the Afghan army and state so that it would be utterly dependent on US support, and later withdrew in such a way as to maximize Taliban advantages (e.g. by demanding the release of Taliban prisoners, withdrawing from bases at night without informing the ANA etc.). On the other side, Taliban has full state support from Pakistan which never wavered and was smart enough to know how to manage them politically (something the US is really really bad at and is at the root of US failure, not just in AfPak). B) Smart warlords knew where the wind was blowing when the US decided to withdraw, and defected to the other side. Oh, and previously, the Afghan president was encouraged to alienate the warlords. Though on this, guilt is only shared, since both Ghani and the US wanted to act so stupidly. C) It's not 75 thousand, that estimate has no legs to stand on, but that's much less important.