The issue isn't having the airlift capability to get stuff to Japan, it's the ability to get the supplies into the hands of the people on the ground. Roads in affected areas are out and quarantine protocols/recommendations will limit the ability to operate in certain areas for extended periods due to radiation hazards.

What they need is a huge fleet of helicopters or COORDINATED air drops, both of which take time to get into place. Just haphazardly dropping supplies into the area can make things worse as people get more and more desperate.