How fast is traditional manufacturing? Sure, once you get your tooling set up and dedicate an entire warehouse to production and assembly, you can crank out ten thousand widgets a day... but it takes months and lots of money to get to that level of production.
Meanwhile, if a part can be 3D printed, you press a button and the next morning you have it in your hand. Client/customer needs some customization? No problem, a day or so of computer time and press the button...
can you 3D print in a moving truck?
Probably. Depends on the printing method. It's not completely certain it would be necessary to print on the go to make this work, though.
is a 3D print product pretty? flexible? neon colors, black, and white are what you have, assuming you are not slinging molten metal or concrete, the other two mediums in use. not flexible.
Full color printers have been available since before most people knew 3D printing was even a thing. Flexible? Could be, with the right materials. Just about anything you can reduce to a fine powder could conceivably be used.
The relatively cheap filament-based machines that are all the rage now are far from the pinnacle of additive manufacturing. 3D printing is 30+ years old at this point. ...All that said, though, I think Amazon's idea is kinda dumb. It's amazing what some people would rather have than money, though.
=Smidge=