Because of the cost of additional eyes. If Tesla is optimizing for cost against safety, that's sort of the point.
I don't believe that's totally the case. Andrej later makes a better argument regarding limited R&D bandwidth, noise and entropy. But the "I would almost reframe the question" evasion was disconcerting. It's a textbook media trained tactic for avoiding a question to which you have no good answer. That it was deployed here badly against a skilled interviewer such that it backfired is a valid observation.
