It's not even about inventory of individual items (like blood or enough scalpels) it's that they need to have every expensive machine. They need x-ray machines and MRI machines and proton beam cancer treatment and that stuff adds up very quickly. That's why a trip to the ER for stitches can cost five figures in the US, because a large amount of that bill is covering the hospital's cost to be ready not just for the stitches but also car crashes or mass shooting events or whatever