Sure, if a car theft for one car spread the cost to _all_ insurance companies, but it doesn't. So to stay competitive, companies have to 1) insure good drivers

Sure, if a car theft for one car spread the cost to _all_ insurance companies, but it doesn't. So to stay competitive, companies have to 1) insure good drivers so the rates stay low and 2) invest in customers who have good car security (note the discount one gets for having their car garaged).