The difference is that GM can afford to absorb the loss while it ramps up production. Tesla needs the Model 3 to be profitable, or the company dies.
[1]GAAP = generally accepted accounting principles. In other words, standardized methods of accounting for profit and loss. Tesla uses non-standard (i.e., non-GAAP) accounting in its financial reports to paint a rosier picture of its financial state than GAAP reporting would provide. Some people say that non-GAAP reporting paints a more accurate picture of a company than GAAP. This might be true for new industries that don't have sufficient history to establish industry-specific GAAP. However, the auto industry has been around for more than 100+ years, so the use of non-GAAP accounting by Tesla and Faraday is generally indicative of unstable financial health.
[2] https://www.forbes.com/sites/alanohnsman/2017/11/01/tesla-pi...
GM could should they choose to do so. They can certainly manufacture them, whereas Tesla's ability is questionable. But one has to sell them once their made. Oh, sure, you might buy a Tesla. Hell, I bought a Leaf, I might buy a Tesla. But you know who won't buy a Tesla? Everyone after the early adopters. GM's been making cars for over 100 years. Odds are really good that a potential customer has owned a GM. Odds are near zero that a potential Tesla customer has owned a Tesla before. For good or for bad, GM is a known quantity. Personally, I go back and forth before laying out money for a $700 phone that is a switch from my current phone. Now scale that up to a $35K car. Maybe you'll just take that out of petty cash from your last liquidity event. The rest of us will scrape together a down payment and hope we can make that monthly nut. And if you're doing that, you're going with the safe bet. The safe bet has a nation-wide network of dealers to work on it, has sold cars for 100 years, and isn't going out of business any time soon. The less-safe bet can't even tell you when you're getting your car +/- six months. In short, when we bought our Leaf, I knew it could easily turn into a $35K mistake, but we have the means and the risk tolerance. I would not make the mistake of projecting that to Mr. and Mrs. Middle America.