I don't get much into the weeds of how everything works in the Middle East.
But I know that ISIS was on the march and expanding during Obama's presidency, then got smoked by the Trump admin. I know that the Taliban was quiet under Trump, then 7 months into Biden's administration they took Afghanistan back.
The build up to war can take a while, but it's not nearly as complex and indirect as, say, the impact of regulatory policy on the economy.
If the Taliban were appropriately afraid they would still be in their holes, and if the US has the political will to stop them they will be stopped. Neither is the case.
Maybe letting the Taliban take over is the "right thing to do" in a realpolitik world, I don't know. But I don't think it's a coincidence that the Taliban waited all the way through the Trump presidency to move even though Trump said from day 1 that he wanted out.