This isn't really surprising; look how long it took them to find S Hussein in a largely desert country.
A couple of years ago I saw some guy called General Ramjet or something talking about how accurate the Air Force's high tech weapons were (I think it was right after they hit a train full of civilians in Bosnia with a laser guided bomb). He basically said that unless the target was standing still, in the middle of a wide open area, undefended, in broad daylight, and wearing a 'BOMB GOES HERE' sign there were no guarantees they could hit it.
A bunch of guys with Kalishnikov's and RPG's outrunning the U.S. military in the snow and ice fog? Highly probable. In December 2001 I suspect angst about incurring casualties in a potentially fruitless search (see above comments on what a target has to look like for them to get it) that would make the military look foolish, outweighed any desire to get Bad Guy #1.
PC
N P Childs
'I'm Mister Bad Example, the stranger in the dirt, I like to have a good time and I don't care who gets hurt'.
-Mr. Bad Example, W Zevon