ventilators are not on every street corner..
Exactly. There are a finite number and they tend to be in use. So it would be relatively easy to overwhelm a healthcare system in an epidemic if many of those affected need ventilators. However, with warning, a hospital can take measures to increase available ventilators by postponing elective surgeries, repurposing ventilators from the OR to patient floors, expediting the repair of broken ventilators, etc. If the people who have the disease don’t need ventilators for very long, this may be enough to keep hospitals from being overwhelmed to the point where they don’t have enough ventilators (or other supplies) for the patients who need them.