For my fiancée and me, we need cargo space for two primary use cases: 1. short-distance hauling of large objects and/or numerous objects, and 2. road trips. It's the frequency of both that encourages the purchase of a large vehicle rather than the rental of one.
In cases of cargo moving (dump dropoff, IKEA pickup, Home Depot), it's typically adult-only trips, so it's really just vacation that's the case where we need a full load of both passengers and cargo. Since vacation is only a few times a year, we figured we'd optimize for the common case and plan to rent a larger van for those instances if necessary, or look at other alternatives, such as a roof box, trailer, whatever.