Whilst 37 x 49mm isn't full frame 645, it isn't as far short as this. 6cm is the full width of the film not the frame width, the frame size of 645 is 41.5 x 56mm. Given the chip yield goes down with about the cube of the size, and given these sensors are already about $10,000 for just the chip, I think they can be forgiven for for the size.
I still shoot 645 film. £35,000 buys one hell of a lot of film, even at the ruinous prices charged now. On the other hand, there is no film around that can achieve the resolution described here. When I win the lottery I will be buying one.