Musk has a reputation for firing senior managers that give him answers he doesn't like, or that fail to meet his unreasonable demands. That level of management meddling doesn't bode well for Tesla's manufacturing future. Nor does "putting parts in the car knowing [they] are bad", if the accusation (by a departed employee) is true. (http://www.wsj.com/articles/elon-musk-sets-ambitious-goals-a...) I have previously questioned, and still do, Tesla's PLM.
Legacy manufacturers do know how to do software, despite the general lousy state of in-car entertainment systems arguing otherwise. They also know how to manufacture a quality product at scale. It's an easier task for them to bolster their software than for Tesla to learn what they already know about manufacturing and ramp up manufacturing.