Most other manufacturers work out the kinks before mass production begins.
How does 20,000 Model 3's in the fourth quarter sound? That's an additional billion in sales just for that quarter. If Musk avoids building another giant plant in the next four or five quarters, their cash burn will drop toward zero rapidly.
If Tesla could demonstrate that they were actually capable of producing 20,000 Model 3's in a quarter, people wouldn't be so pessimistic. As it stands, they're still struggling to produce a few hundred cars a quarter without serious quality control concerns, and they've missed every self-imposed target for several years straight. (Tesla reported roughly 2500 Model 3s in all of Q4. For comparison, most other manufacturers can produce more cars than that in a single day.)