TL;DR the time and investment it takes to perfect fully automated car production is still prohibitive and has a poor return on investment. GM learned this the hard way in the 80s and Tesla is getting the same hard lesson now.
You didn't read until the end of the article. For instance:
> "Musk likely could have spared himself a lot of short-term headaches if he had relied more heavily on auto industry veterans to warn him against repeating mistakes made by other car companies in previous decades. But if he had done that, he would also be less likely to discover ways to optimize the manufacturing process—particularly optimizations that work particularly well for a company specializing entirely in electric vehicles."
