Tesla chose carbon fiber for its strength and light mass. However, the material is expensive to produce. I had hoped Dickinson would have explained more of the decision-making process and what the alternatives were, but carbon fiber is the most appropriate choice for this application. Again, the only downside is the cost, and we all want more people, not fewer, driving electric vehicles.
Tesla is keeping the cost down a little by using a Resin Transfer Molding (RTM) process in place of the traditional autoclave curing. This is a type of closed-mold process that requires significant tooling but can produce body panels quickly and to the required thickness. Plus, the panels come out of the mold already primed for paint.
The one big hurdle Tesla had to overcome was their sources of carbon fiber cloth were drying up. Apparently the demand in the aerospace industry is skyrocketing. But persistence paid off and the Tesla is nearing production.