Been thinking about it. That's my opinion.
Not because of the human rights issues, as bad as they are.
Not because the US looks like it has the habit of losing the peace after it wins wars.
Not because the Afghan government and military was so flimsy.
Not because of the poorly planned exit.
It's the issue of providing a safe place for AQ to regroup. The risks of staying were lower than those of leaving. The costs of staying were also small.
That isn't the benefit of hindsight. It doesn't depend upon the events of the last week. It's been true for 20 years. And Biden has provided no compelling reason why the threat no longer exists.