Because if they break down in the middle of nowhere, or on the highway, they get towed to a shop. If they run out of gas, or get a flat tire...or lock their keys in the car, AAA comes out and rescues them. THAT'S why people would want to have AAA. And this works even if you are in someone else's car...it's a no-brainer. And if you're traveling, they give free "trip-maps" that gives you a map with points of interest along the way.
Why do you care what people elect to do as this service or any automobile service organization? Have you read the benefits and services offered?
Why not?