There are real world limitations.
A silicon wafer and the masks used to make the chip have a high price, which has to be divided over units sold. The larger the sensor, the fewer sensors can be made out of it. Then, the larger the sensor, the fewer the cameras sold. This means higher price per unit.
Wafers aren't clean. There might be dozens of defects (in the silicon itself, dust particles, etc) on it. The larger the chip, the higher the chances there would be a defect in its area, so the number of chips that can be made out of a wafer drops exponentially with its size.
Which is why the
Hasselblad H6D-400C's sensor costs $26,000.
450mm wafers are on the horizon, which might lower sensor prices. Then again, the market is shrinking. I would be surprised if digital 645 would become viable option in the next 25 years.