In times past, most dealers and their digital advertising providers believed in a bulk, wide-net mentality when it came to venues such as search PPC and banner advertising. That strategy is quickly starting to die down thanks to a more competitive atmosphere driving up prices and emerging technology that makes targeting much easier. Today, dealers don't need to cast a wider net. They need to make sure their nets don't have any holes in them even if that means casting a smaller net.
On DrivingSales, a blog post points to the advantages of making sure that targeting is the most prevalent aspect of advertising spends. It's not about getting in front of everyone. It's about getting in front of buyers who can come by the dealership today. Otherwise, it's better to spend all of the budget on television and radio.
At first glance, it's an easy question with an instant answer. Car dealers want to target everyone within driving distance with their message. As Ripley said in Aliens, "It's the only way to be sure."
Upon closer examination, problems start to pop up. Even if we assume that "everybody" is actually a large portion of the audience (since you can't reach everybody from a literal sense), there are still holes in the strategy. Those who have extremely large marketing budgets could do it, but even then they really shouldn't.