Well, according tp the American Red Cross, their presence would have kept people from evacuating and encourage others to come into the city.
Besides:
Quote:"We are an organization of civilian volunteers and cannot get relief aid into any location until the local authorities say it is safe and provide us with security and access.
The original plan was to evacuate all the residents of New Orleans to safe places outside the city. With the hurricane bearing down, the city government decided to open a shelter of last resort in the Superdome downtown. We applaud this decision and believe it saved a significant number of lives. "
Source
In exchange, why weren't planes from Germany, the UK and Russia allowed to land in the USA? (The German food, 25 tons, HAD been distributed in NO before .... and as well to US soldiers in Afghanistan AND was asked by the US ambassador.)