Just imagine the corrupt mess the US supported government in Afghanistan must have been if the Afghani's prefer the Taleban over democracy.
How do you know? And for those that prefer Taliban, how do you know why they prefer them? Corruption is your assumption, but they might just like the ruthless Islamism of the Taliban.
Sweden has a pretty significant Afghani population today. I listen to an ex-Muslim Swedish podcast. One of them is Afghani. His family still lives in the country. They talk. Afghanistan isn't an insular little bubble where no information gets out. We know a lot about the situation for Afghanis.
The Taleban are back in power because they're the least bad option for most Afghanis. It's as simple as that. We can debate why that is. But the moment US money stopped propping up the old regime it switched sides in an eye blink and joined the Taleban. Ie, they were Taleban supporters all the time. Only opportunistically pretending to support to US regime, and lining their pockets.
You are aware that they Taleban hasn't had to fight anywhere in Afghanistan? They're very popular in the country. Which annoys secularists like me. But everybody isn't a secularist. A lot of people are deeply conservative and religious.
Have you never wondered how come all the leading Afghanis in the US supported regime spent their adult lives outside Afghanistan, comes home the moment USA is in power and then get prominent positions in the new regime. Locals didn't seem to get anywhere in the political hierarchy.
edit:
I don't know if you remember this, but around 2004 it emerged that Osama Bin-Laden was just a guy living in Afghanistan. He wasn't supported by the state, nor was part of an organization. Al-Qaeda wasn't an organization. It was just Ayman al-Zawahiri, who Bin-Laden gave money in order to spread his ideology. And the little group around him. The 9/11 hijackers were all Saudis Osama knew from his time there. They had a lot of money, thanks to Osama. But they were never a popular movement.
US state prosecutors needed Al-Qaeda to be an organization in order for their anti-terror legislation would allow them to effectively combat Bin-Laden. So they invented the organization Al-Qaeda. Various Islamist terror groups then started using the name, with zero connection to Ayman al-Zawahiri.
al-Zawahiri and Bin-Laden's theory was that that 9/11 would trigger a world wide Muslim uprising that would lead to the re-establishment of the Caliphate. Well... that didn't pan out. It turned out that Ayman al-Zawahiri had about zero pull among the Muslim mainstream. His world wide uprising died out almost immediately. By 2003 Ayman al-Zawahiri's dream and Al-Qaeda was dead.
After that all that remained were it's ghosts. The war on terror was only ever a war on a ghost from the past.
I supported the war in Afghanistan and the ousting of the Taleban. Good riddance IMHO. But the regime to replace it was harder to build. In hindsight it turned out that perhaps maybe, we should have just let the Taleban be left alone. We know now they weren't hurting anyone outside Afghanistan. They can't be held accountable for what two guys (Ayman al-Zawahiri and Osama Bin-Laden) did in their remote mountains.
I'm pretty sure ISIS was as much a surprise to Ayman al-Zawahiri and Osama Bin-Laden as everybody else.
The Islamist "conspiracy" is, and was always, an utter complete mess. A headless chicken.