Talk to someone with military experience about the logistics that would have been involved in a large-scale ground operation in Afghanistan.

Look at the history of such operations, like Desert Storm, or the invasion of Iraq. Both involved heavy buildups over a long period of time prior to the invasion.

Afghanistan HAD to be attacked by air, and with only small, rapid-deployment forces on the ground. Otherwise, by the time the invasion commenced, every last terrorist would already have been in Pakistan. As it is, we got a lot of them. Just not all of them.

Remember that in history, most ground invasions of a country involved taking territory and destroying fixed assets and heavy armies. How many times has a major battle commenced in which the objective was to nail a specific, small group of mobile people inside the territory?

In other words, the "not enough troops during the attack" thing is now, and has always been, a red herring. It's another part of the myth that Someone Else Could Have Done Better.