It was originally supposed to be an exoskeleton of folded metal.

This informed the whole design, it would lead to a lightweight, low cost truck that could be delivered with the battery tech available at the time. They highlighted not painting it as a cost saving move at the reveal.

Then they gave up on that idea as unworkable, but kept the look, so it's like designing a bit of furniture around some fancy solid wood steam bending technique then trying to fake it with wood laminate.

It was also delayed so long that other truck manufacturers just used the cheaper batteries available by then to make competitive trucks based don standard truck bodies.