Why were Emergency Dispatch Ships created?

Tom Godwin’s “The Cold Equations” is a futuristic story that presents a moral dilemma. In this futuristic setting, mankind has expanded to other worlds. Large ships called cruisers carry colonists to far away planets using hyperdrives that make distant travel possible.
However, there are not enough cruisers to administer to the colonies in the event of emergencies. An EDS is an “emergency dispatch ship.” The EDS’s are used to deliver emergency supplies when colonies have an unscheduled need.
In “The Cold Equations” the EDS is travelling to Woden to deliver a serum for a fever that has broken out. Unfortunately, a young girl has stowed away on the EDS, hoping to visit her brother on Woden. She is unaware that the EDS only carries enough fuel to deliver its cargo and return to its cruiser. Her extra weight will cause the EDS to crash if she is not jettisoned. Near the end of the story, that is just what happens.