Why? I mean, if the Starship is reusable, and they're producing enough engines to build 2-4 a month, that seems like overkill. How many Starships are even needed?
Enough to get a million metric tons of cargo to Mars (the estimated minimum for viable long term settlement, as explained elsewhere in comments) on a reasonable timetable.
The most comparable scale they’re targeting for manufacturing Starships is jet airplanes. They’re supposed to be space busses, essentially. The way Musk sees them is, as “cattle, not pets”.
Elon wants >1,000 Starships due to the Mars launch window, every 2 years. He wants to get a million+ tons of stuff there quickly. At 100T per Starship, and 1,000 starships, it would take at least 20 years to get 1M tons there.
So, Starship will be really cheap because they are reusable. Also, Starship will commit a larger fleet than all the planes that Boeing and Airbus combined make in a year to a more two decade long mission.
I'm not saying it's impossible, but it does mean SpaceX will really have to scale up. Where is that capital going to come from? I'm not even sure even with all of Musk's personal assets and selling out on launches they'll get there for decades.
