Does Tesla want the big automakers to build cars with equal capabilities as the Model S? Assuming they did so, would they not be more cost-competitive due to economies of scale? Their mission of promoting sustainable transporation might be at odds with their fiduciary duty to their shareholders then.

If Tesla really wanted to see the big auto makers build more capable electric cars, AND if they also want to be a profitable enterprise, THEN, the best course of action would be to OEM the powertrain parts that they have already invested in inventing and building.