What most are apparently missing is the keyword in the name. This is a PRO device that few consumers would (or could) buy, just as is the Mac Pro - a computer not needed or affordable by most. I suspect that we will see the "non-pro" device once the hardware and software is proven and matures.
So why not start at the bottom and work up, just as was done with the M1 line? Because Apple is pushing the state of the art big time with this and has probably just barely carried the ball over the "Hey, it is finally working!" line. If they could make these right now for a retail price of, say $999, the plants would be in full production.
I am old enough to remember the predictions that color TV was a fad that would peak, then disappear. They cost too much, had lousy pictures, no available programming, could not be bumped even slightly without causing a service call... Had anyone said that one day you could get a 75 inch color TV that was an inch thick and cost (in 1960 dollars) about fifty bucks... Well, in those days the media had actual editors. They would not even have printed such nonsense.
If this device has a use that is wanted by the average person, mass production will bring the cost down just as it has done for everything else.