For most cargo vans there is a wall that separates the cargo from the cab. In some places this is a legal requirement to help prevent injury from loose cargo during an accident. Even without a partition I don’t see how sharing the cab with cargo is less useful, maybe more dangerous but not less useful.

Fuel economy used to be much worse for trucks vs vans but with modern vehicles they even out more and many smaller vans have a better fuel economy than a light pick up truck.