what to do with excess donations

When there is a highly-publicized disaster, relief agencies typically get more donations than they need for that particular disaster. But they don't get enough for other disasters. I, like many others, have been motivated to donate at times of well-publicized disasters. But I never designate my donation for a particular disaster. I will designate for "disaster relief". That, the agency can use my donation where it's really needed. I don't understand people who get upset when more donations are received for a disaster than are needed by the agency, and the agency uses them for other people in need.