Because they're trained first-responders, who have medical first aid training, vehicles with lights and sirens to move quickly through traffic, knowledge of the local area to navigate around road closures or ambiguous location descriptions, etc.
There are many situations where multiple sub-specialties of first-responders (police, firefighters, EMT, etc) are useful. The police aren't just showing up to arrest or shoot people, in a functioning society they can and do provide valuable service in assisting injured people, controlling traffic around car accidents, etc.