A ford Transit van fits that requirement much better - much more useful as a utility vehicle, much more space for advertising, much cheaper...

Outside of certain kinds of construction contractors, I rarely if ever see pickup trucks used for this purpose.

This anecdote might indicate why: We recently had a bunch of work done on our house. The siding crew had a pickup truck, and every morning the very first thing they did was unload the entire contents of the truck into our back yard. The plumbers and electricians would just get the stuff they were actually using and then lock the van.