Everybody's trying. This is a pretty unique situation. The area that needs help is almost completely inaccessible due to water, and is surrounded by other hard hit areas which are being stretched to the limit just to sustain their own.
As someone who works in NYC, and was here (in midtown) on 9/11, I don't have any trouble seeing the huge difference between the two situations. NYC had plenty of food and water, the vast majority of people were able to walk home (even if a long way) after subway service was stopped and bridges and tunnels closed for security reasons to a home with food, clean, running water, electricity, and access to Internet/radio/TV/phone. Those who couldn't get home stayed with friends in fully functional homes. There were more able-bodied volunteers than were needed -- a licensed EMT friend of mine tried to volunteer but wasn't needed. The closing of bridges and tunnels was brief enough that store shelves were never anywhere near empty.
Only a tiny fraction of New Yorkers who survived the initial attack were in any mortal danger from injuries, being trapped etc. Most of us were physically fine, and just a bit wary about whether that would continue. I was pretty typical -- walked 40+ blocks to get home, stopping by the grocery to pick up bleach and candles and extra food that wouldn't require refrigeration, and the hardware store to pick up 3 large plastic trash cans for water storage. Went home, filled up my new water tanks, put away my stock of food, ate a nice dinner, and sat down in front of my computer to follow the situation closely via FR and other sources in my air conditioned apartment. Exchanged e-mails with a shaken-up friend who worked downtown and saw the 2nd plane hit as she emerged from the subway and then had to run for her life through the cloud of dust as the first tower fell (she'd managed to get home to New Jersey, with the last leg of her trip on a passing fire truck that picked her up and delivered her to the front door of her building). I never needed the stored water or non-refrigerated food. The next night around midnight, my 20-something-year-old cat needed an emergency trip to the vet hospital, and we hopped in a cab (driven by a Muslim who was chattering angrily, describing the attackers with streams of expletives) and went on our way. The VET hospital (the huge Animal Medical Center) was fully functioning, even after dispatching as many as vets and vet techs as the search and rescue dogs at the WTC site needed, though the air was a bit smoky from the wind having shifted to blow uptown.
Sorry, but the 9/11 situation in NYC was NOTHING like what the people of New Orleans are currently experiencing.
The point is plenty of help poured in from all over...It has been confirmed that people are now dying in the dome of dehydration. This is America; we are not a third world country. Food and Water could be dropped in by aircraft. There is not-nor ever will be- any excuse for this situation.