The wikipedia article about paramedics gives insight into this.

A key quote: "In 1966, a report called Accidental Death and Disability: The Neglected Disease of Modern Society—commonly known as The White Paper—was
published in the United States. This paper presented data showing that
soldiers who were seriously wounded on the battlefields during the Vietnam War had a better survival rate than individuals who were seriously injured in motor vehicle accidents on California's freeways."

This eventually led to equipping ambulances with life saving equipment and trained paramedics. This started in the US in the late 60s and early 70s, and has spread to the rest of the world.