Well, despite the name of this forum, a cargo bike is not a utility bike. A cargo bike is intended to carry heavy and/or bulky loads.
A utility bike is intended for running errands by a not too skilled rider. The classic three speed is the model it derives from and is really intended for trips of 5 miles or less in traffic. For that the semi-upright position gives a good view of surrounding traffic without requiring the riding skill that dropped bars do.
Cycle couriers usually ride a road bike converted to a single speed, given a choice, they usually are extremely fit very experienced bicyclists. They like single speeds because they need reliability and they do not usually need to climb hills.
There is no reason you can not build a long haul cargo bike with dropped bars, etc. But if you are going to be moving slowly in heavy traffic you probably would want the semi-upright riding position for the same reasons a utility bike rider would.