IIRC, part of the goal was weight reduction, which is a significant consideration with EVs. If you can convert the cosmetic body panels into structural element

IIRC, part of the goal was weight reduction, which is a significant consideration with EVs. If you can convert the cosmetic body panels into structural elements, you can reduce the overall bill of materials. They have since aggressively pursued large cast aluminum frame technology. This reportedly reduced the complexity of their car's frames from 100+ pcs down to 1 or 2. My guess is that they switched the trucks fully over to these Al frames as a way to homogenize their production lines. Purely conjecture, but they probably held off under the assumption that they could not produce the Al frames fast enough, but a sales slump freed up the production capability.