During those two decades the country was operating under a western puppet government. The fact that the Taliban swept in so quickly with no resistance means that they were always there to begin with.
For several elections it's hovered around the 1/3 mark. That's not bad by regional standards, and bear in mind several large and populous regions in Afghanistan are non-Pushtun and even follow different branches of Islam. There's just no way the Taliban can conceivably command anything more than middling minority support.
They just have more guns and a bloodier determination to use them. Unfortunately, as is often the case, that’s all it takes.