This is an often repeated media trope that seems a bit misleading. It makes it sound like they would loose more money if they sold more cars. That is not true. Tesla has positive gross margins.
Tesla is investing in future production and that is part of why it is losing money. I would also draw your attention to a strange fact about GAAP accounting principles. Some investments like the GigaFactory are depreciated and the expense is spread over the lifetime of the operation of the factory. However, R&D, although it’s an upfront cost that pays off over the long term, is not depreciated. You take the full charge in the quarter the money was spent. I suspect it’s because R&D has a less predictable payoff and timeframe than an investment in a hard asset like a factory.
Another factor in Tesla’s lack of profitability is their high sales expenses (SG&A). Currently SG&A is about 20% of non-gaap revenue. At most auto companies it’s about 10%. The number of Model 3 preorders indicates that their current sales infrastructure is scalable and can support much larger revenues. At scale SG&A is likely to be a lower percent of revenue.