As an example, my aunt just recently had a heart attack about two weeks before this covid stuff and had to be put on a ventilator. While in the ICU she developed an infection from a rare fungal disease that had been in her lungs for a while but suddenly had the opportunity to grow and cause respiratory distress. A lot of people have strange microbes in them that are being held at bay by the immune system. When all of a sudden you expose an already immuno-distressed person to someone else's novel microbes, you risk opportunistic infections, even in non-covid patients.

I'm sure they can figure out how to re-use ventilators, but there probably needs to be some kind of assurance so that things can't cross.