True enough... But just as they used the "2nd Commando Brigade" (Iraqi?) to secure buildings pre-strike, I'm betting we have a few similar folks moving about, collecting intel.
But the more units you have moving about, the harder it is to keep track of them and where they are, the harder it is to provide support in case they run into superior forces..
Such roving units have to be kept close track of and that necessitates limited numbers..