The body is made of stainless steel, which is bad for several reasons.
Because it's stainless, it can't be stamped, but it still must be shaped. Stainless steel is very difficult to bend into the proper shape. It's also expensive.
The article brings up another point I hadn't considered; stainless is tough to bend and crumble. Modern cars are designed to bend and crumble (in a controlled way) in an accident. This keeps the occupents safer because the more of the collidion's energy is spent crunching the car, the less is transferred to the people inside. A Cybertruck will survive a crash with only a scratch, but its occupants will be paste.
This is example #2739 of Musks ego getting in the way of design. He is so intent on proving to the world that he can design a truck from scratch that he doesnt bother to learn industry practices, some of which are there for good reason.