Steve, I suspect the problem is availability of nets and slings, as well as competent ground handlers/marshallers. If you have the supplies in the aircraft then you can land anywhere and hand out the goodies before moving onto the next place - if you have a netted load it will all have to be dismantled before you can move on or you will have to come back for the net and strop later which both add time to the distribution of the aid. You also have to assume that at the distribution centre there are enough qualified people to prepare the loads safely and keep a safety check on the nets and strops.