Because they're not there to help

A firm tries to use UAVs in ways that are undeniably good and gets shut down by the U.S. Federal Emergency Management Agency (FEMA) (Wired). Kind of depressing:

There's been some terrible, terrible flooding going on in Colorado. Rain is still falling, making it difficult (or impossible) for airplanes and helicopters to get in and out of the area. Drones can fly, though, and while they're not able to pick up people or drop off supplies, they are able to make damage assessment maps to help relief agencies coordinate their efforts. Or at least, they were, until the U.S. Federal Emergency Management Agency (FEMA) showed up and grounded them.