Also, obligatory: staff. Which is to say the health care system is sized for employing enough highly-trained trauma / ICU staff to support normal operations, wi

Also, obligatory: staff. Which is to say the health care system is sized for employing enough highly-trained trauma / ICU staff to support normal operations, with some small (very small) amount of surge capacity. And people under-estimate the specialization & experience required for high-level ICU and respiratory care. You can't just take a floor nurse and transfer them over to do the new work. And the amount of complex hospitalizations due to COVID can very quickly become a couple orders of magnitude above "normal operations."