Many of them have nothing up their sleeve.... "Body parts everywhere!"....
Well, practically speaking, because the bad guys probably still needed to use the buildings. Boobytrapping a building is a double edged sword; it can accidentially kill the bomb maker or his buddies before the targets get to the the site. Plus, with the rapid rate of advance of the U.S. forces, it might be tough to set those bombs while running from an Abram's tank, Styker, or the other raghead shreaders operating out there.
On the other hand, there were a fair number of mines in the approaches, which our engineers defeated in the first 30 minutes of the assault. Plus, our guys aren't going house to house, only at strategic intersections, bridges, and so forth, where they need to secure an area. Otherwise, if there's a bunch of bad guys in a building shooting at our guys, they lay down precision artillery or airstrikes and level the buildling.
The Jahidi's (also known as "Muslim faithful") may have some sewers and tunnels we haven't yet blown up, but mostly they're either dying in place, or dying on the run. I haven't heard of many prisoners being taken, but I suppose there are a few of those also.
SFS