Because they give a more "wrap around" view, thus cutting down on blind spots.
convex mirrors are used in vehicles because convex mirrors make things look bigger which will be easy for the drivers.
Concave mirrors are used in telescopes. Convex mirrors are used as side-view mirrors in cars.
Convex mirrors
Convex mirrors are often used for side mirrors (if the mirror has a note saying "objects in mirror are closer than they appear," it's convex; it may be convex even without such a note).
Convex mirrors
convex mirror
To give a wider angle of view.
convex mirrors are bent outward,hence can provide the full view of the traffic behind the car and are preferred to concave and plane ones
Convex Mirror
Convex mirrors are used as driving mirrors because they give drivers a much larger field of view without needing to move their heads from side to side.
convex mirrors are used as it reflects the sunlight efficiently and produces more heat
The Rear view mirrors are convex The Headlights are concave