...It was 16 years because nobody had the stones to do it the right way: go in, sterilize the place, and leave-done in a few months...
It would have been much easier to nuke that $hithole, but politically impractical.
As an alternative...
We should have done a much better job at Tora Bora and not let Osama bin Laden slip across the mountain passes into Pakistan.
We should have killed the sonofabitch then-and-there, slaughtered as many Taliban and leveled as many Taliban strongholds as we could, then just walked away...
Leaving them stumbling-about in the smoking ruins, rather than trying yet another round of doomed-to-fail Nation Building, which we are not very good at.
We were able to Nation-Build in both Germany and Japan because we were dealing with formerly-civilized people grounded in civilized belief-systems.
We haven't been very successful at Nation Building either before or after those two successes, and we should really stop trying.
Especially when dealing with Mountain Goat Buggerers practicing a vile 1300-year-old Warrior Cultism that's kept them in the Dark Ages into our present time.
Hammering Afghanistan was a 'Righteous Shoot'.
But we should have been in-and-outta there inside of six months.
Every 7-year-old kid playing backyard cops and robbers knows to put a couple of kid-cops in back of the garage, to cut off the bad guys' escape route.
Why-the-hell our tactical planners didn't park a couple of airborne battalions in the mountain passes to cut off Tora Bora survivors fleeing to Pakistan is beyond me.
Maybe we should have let a 7-year-old kid do the planning on that one.