My hunch is that they can only show a tiny percentage of the footage being shot.
My hunch is that they don't have that much footage. For the first few days they just showed the same clips over and over. It seems that the cable channels don't really have huge teams of reporters or a lot of equipment in scene. They just buy footage from local stations.
What really cracked me up is how MSNBC has one of their anchors doing a show on New Orleans "live and direct from Aruba".