I have made the same point about our evacuation from Saigon in which several servicemembers died during the confusion and chaos.

Trump negotiated without the afghan govt effectively stabbing them in the back such that the Afghan military simply left- why keep fighting?

I do not fault Biden for the evacuation - and especially not for the deaths of US soldiers. A suicide bomber is impossible to stop without good intelligence. The bomber was not taliban but another rival radical . So the taliban had not intelligence either as they guarded the perimeter of the evacuation.