Why do acts of bioterrorism or natural disasters often have more casualties?

A. Those with chronic conditions cannot escape in time: While this is a risk for some, it does not explain the overall high casualty rates. B. Victims have little time to make evacuation preparations: Lack of warning and rapid onset are key reasons for higher casualties during bioterrorism and natural disasters. C. The early warning systems are not effective: While this may be true in some cases, the main issue is often the limited time to respond, not system failure.