Masks and valves and tubing are much less durable goods than the ventilator itself; some of them wear out, some of them become biohazards after use, etc. So the

Masks and valves and tubing are much less durable goods than the ventilator itself; some of them wear out, some of them become biohazards after use, etc. So there's both a shortage of the parts required to keep existing ventilators in continued use, and of the machines themselves.